Thermoplastic resin composition, optical film and retardation film

ABSTRACT

Each of the thermoplastic resin composition and the optical film of the present invention comprises a cycloolefin-based polymer (A) and a vinyl-based polymer (B) having a structural unit derived from p-isopropenylphenol. The thermoplastic resin composition and the optical film exhibit excellent compatibility of their components with keeping property of low birefringence inherent in the thermoplastic resin composition comprising the cycloolefln-based polymer and the vinyl-based polymer, and they are excellent in weathering resistance and heat resistance.

TECHNICAL FIELD

The present invention relates to a thermoplastic resin compositioncomprising a cycloolefin-based resin and a p-isopropenylphenol-basedcopolymer, and an optical film. The present invention also relates to aretardation film obtained by stretch-orienting the optical film.

BACKGROUND ART

Cycloolefln-based ring-opened (co)polymers have merits such that theyhave high glass transition temperatures attributable to rigidity of themain chain structure, they are amorphous and have high lighttransmittance because a bulky group is present in the main chainstructure and they exhibit property of low birefringence because ofsmall anisotropy of birefringence, so that they have been paid attentionas transparent thermoplastic resins having excellent heat resistance,transparency and optical properties.

The conventional cycloolefin-based ring-opened co polymers, however, donot have sufficiently low birefringence value, and accordinglydevelopment of thermoplastic resin compositions having more excellentproperty of low birefringence has been desired.

In a patent document 1, a thermoplastic resin composition comprising acycloolefin-based resin and an aromatic vinyl-based (co)polymer having apolar group is disclosed. It is also disclosed that this thermoplasticresin composition exhibits lower birefringence as compared with theconventional cycloolefin-based resins. The thermoplastic resincomposition described in -he patent document 1, however has a problem oflowering of weathering resistance and heat resistance though it exhibitsproperty of low birefringence.

In patent documents 2 and 3, a thermoplastic resin compositioncomprising a cycloolefin-based resin and a polystyrene-based polymer isdisclosed. In the patent documents 2 and 3, however, ap-isopropenylphenol-based copolymer is not disclosed as thepolystyrene-based polymer.

In recent years development of various optical films has been made bytaking advantage of features of cycloolefin-based resins orthermoplastic resin compositions containing them. Such optical films areusually produced by a solvent casting method using a solution obtainedby dissolving a cycloolefin-based resin or a thermoplastic resincomposition containing the resin in a solvent. For example, in thepatent document 2, a transparent film is produced by casting a solutionthat is obtained by dissolving a thermoplastic resin compositioncomprising a cycloolefin-based resin and a polystyrene-based polymer inmethylene chloride using a compatibilizing agent. However, when athermoplastic resin composition is dissolved using a compatibilizingagent, compatibility in the thermoplastic resin composition needs to becontrolled, and this controlling operation is troublesome. Further, thecompatibilizing agent remains in the resulting film, and therefore, filmproperties are sometimes deteriorated. Moreover, a retardation filmproduced by the use of the compatibilizing agent is sometimesdeteriorated in the appearance of retardation.

If the thermoplastic resin composition is dissolved in methylenechloride without using methylene chloride compatibilizing agent, phaseseparation takes place to give an opaque film. In the case where thecompatibilizing agent is not used, therefore, it is necessary todissolve the thermoplastic resin composition in toluene having higherdissolving power. However, toluene has a high boiling point and has anevaporation rate of about 20 times the evaporation rate of the methylenechloride, so that in case of a solvent casting method, the drying timebecomes long, resulting in a problem of low film productivity.

Patent document 1: Japanese Patent Laid-Open Publication No. 323098/1999

Patent document 2: Japanese Patent Laid-Open Publication No. 194527/2001

Patent document 1: Japanese Patent Laid-Open Publication No. 337222/2001

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention is intended to solve such problems associated withthe prior art as described above and it is an object of the presentinvention to provide a thermoplastic resin composition which exhibitsexcellent compatibility of its components with keeping property of lowbirefringence inherent in the thermoplastic resin composition comprisinga cycloolefin-based polymer and a vinyl-based polymer and further hasexcellent weathering resistance and heat resistance. It is anotherobject of the present invention to provide an optical film comprisingsuch a thermoplastic resin composition and a process for producing theoptical film. It is a further object of the present invention to providea retardation film which keeps excellent appearance of retardation andis excellent in weathering resistance and heat resistance.

Means for Solving the Problems

In order to solve the above problems the present inventors haveearnestly studied, and as a result, they have found that a thermoplasticresin composition comprising a cycloolefin-based polymer and avinyl-based polymer having a structural unit derived fromp-isopropenylphenol has property of low birefringence and excellentcompatibility of its components and is excellent in weatheringresistance and heat resistance. Based on the finding, the presentinvention has been accomplished. The present inventors have furtherfound that a retardation film obtained from the thermoplastic resincomposition exhibits excellent appearance of retardation, weatheringresistance and heat resistance. Based on the finding, the presentinvention has been accomplished.

That is to say, the thermoplastic resin composition of the presentinvention comprises:

(A) a cycloolefin-based polymer, and

(B) a vinyl-based polymer having a structural unit derived fromp-Isopropenylphenol.

The cycloolefin-based polymer (A) preferably has a structural unitrepresented by the following formula (1)

wherein R¹ to R⁴ are each independently a hydrogen atom, a halogen atom,a substituted or unsubstituted hydrocarbon group of 1 to 30 carbon atomswhich may have a linkage containing oxygen, nitrogen, sulfur or silicon,or a polar group; R¹ and R², or R³ and R⁴ may be bonded to each other toform a monocyclic or polycyclic carbon ring or hetrocyclic ring; X isindependently —CH═CH— or —CH₂CH₂—; m is 0, 1 or 2; and p is 0 or 1.

The vinyl-based polymer (B) preferably further has a structural unitderived from an aromatic vinyl-based monomer other thanp-isopropenylphenol, and more preferably further has a structural unitderived from a vinyl cyanide-based monomer.

The optical film of the present invention comprises:

(A) a cycloolefin-based polymer, and

(B) a vinyl-based polymer having a structural unit derived fromp-isopropenylphenol.

The retardation film of the present invention is obtained bystretch-orienting the above-mentioned optical film.

EFFECT OF THE INVENTION

According to the present invention, a thermoplastic resin compositionand an optical film each of which exhibits property of low birefringenceand excellent compatibility of its components and is excellent inweathering resistance and heat resistance can be obtained.

By stretching the optical film, a retardation film exhibiting excellentappearance of retardation and having excellent weathering resistance andheat resistance can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general view of a ¹³C-NMR spectrum of a copolymer (2) usedin the working example.

FIG. 2 is an enlarged view of FIG. 1.

FIG. 3 is a view showing results of differential scanning calorimetry ofa transparent film obtained in the working example.

BEST MODE FOR CARRYING OUT THE INVENTION

The thermoplastic resin composition and the optical film of theinvention comprise (A) a cycloolefin-based polymer and (B) a vinyl-basedpolymer having a structural unit derived from p-isopropenylphenol.

(A) Cycloolefin-Based Polymer:

The cycloolefln-based polymer for use in the invention preferably has astructural unit represented by the following formula (1)

wherein R¹ to R⁴ are each independently a hydrogen atom, a halogen atoma substituted or unsubstituted hydrocarbon group of 1 to 30 carbon atomswhich may have a linkage containing oxygen, nitrogen, sulfur or silicon,or a polar group; R¹ and R² or R³ and R⁴ may be bonded to each other toform a monocyclic or polycyclic carbon ring or hetrocyclic ring; X isindependently —CH═CH— or —CH₂CH₂—; m is 0, 1 or 2; and p is 0 or 1.

As the cycloolefin-based polymer for use in the invention there can bementioned for example,

(i) a ring-opened polymer of a cycloolefin-based monomer represented bythe following formula (2) (referred to as a “specific monomer”hereinafter):

wherein R¹ to R⁴, m and p have the same meanings as those in the formula(1),

(ii) a ring-opened copolymer of the above specific monomer and acopolymerizable monomer,

(iii) a hydrogenated (co)polymer of the ring-opened (co)polymer (i) or(ii),

(iv) a (co)polymer obtained by cyclizing the ring-opened (co)polymer (i)or (ii) by Friedel-Crafts reaction and then hydrogenating the reactionproduct, or

(v) a saturated copolymer of the above specific monomer and anunsaturated double bond-containing compound.

As the cycloolefin-based -polymer having a structural unit representedby the formula (1), there can be also mentioned, for example,

(vi) a homopolymer obtained by ring-opening copolymerizing adicyclopentadiene (DCP)-based monomer represented by the followingformula (3) and then hydrogenating a 5-member ring:

wherein R⁵ to R⁷ are each independently a hydrogen atom, a halogen atom,a substituted or unsubstituted hydrocarbon group of 1 to 30 carbon atomswhich may have a linkage containing oxygen, nitrogen, sulfur or silicon,or a polar group,

(vii) a hydrogenated copolymer of a ring-opened copolymer of the abovespecific monomer and the above DCP-based monomer, or

(viii) a hydrogenated copolymer of a ring-opened copolymer of the aboveDCP-based monomer and a copolymerizable monomer.

The specific monomer, the copolymerizable monomer, the unsaturateddouble bond-contain ng compound and the DCP-based monomer can be eachused singly or as a mixture of two or more kinds.

Of the above (co)polymers (i) to (viii), the hydrogenated (co)polymer(iii) or (vii) is preferable, and the hydrogenated (co)polymer (iii) isparticularly preferable.

The cycloolefin-based copolymer (A) for use in the invention is desiredto have a polar group from the viewpoint of compatibility with thevinyl-based polymer (B).

Next, R¹ to R⁷ in the formulas (1) to (3) are described in detail.

Examples of the halogen atoms include a fluorine atom, a chlorine atomand a bromine atom.

The hydrocarbon group of 1 to 30 carbon atoms is, for example, a grouprepresented by the following formula:

—(CH₂)_(m)—R′

wherein R′ is a cycloalkyl group, such as cyclopentyl or cyclohexyl, oran aryl group, such as phenyl, naphthyl or anthracenyl, and m is aninteger of 1 to 10.

Examples of such hydrocarbon groups include alkyl groups, such asmethyl, ethyl and propyl; cycloalkyl groups, such as cyclopentyl andcyclohexyl; alkenyl groups such as vinyl, allyl and propenyl; alkylidenegroups, such as ethylidene and propylidene; aryl groups, such as phenyl,naphthyl and anthracenyl; and aralkyl groups such as benzyl and2-phenylethyl. Hydrogen atoms bonded to carbon atoms of these groups maybe replaced with halogen atoms, such as fluorine, chlorine and bromine,a phenylsulfonyl group, and a cyano group.

The above substituted or unsubstituted hydrocarbon group may be directlybonded to a ring structures or may be bonded thereto through a linkage.The linkage is, for examples a divalent hydrocarbon group of 1 to 10carbon atoms (e.g., alkylene group represented by the formula (CH₂)_(m)—wherein m is an integer of 1 to 10), or a linkage containing oxygennitrogen, sulfur or silicon (e.g., carbonyl group (—CO—), carbonyloxygroup (—COO—), oxycarbonyl group (—O(CO)—), sulfonyl group (—SO₂—),sulfonyloxy group (—SO₂O—), oxysulfonyl group (—OSO₂—), ether bond(—O—), thioether bond (—S—), imino group (—NH—), amide bond (—NHCO—,—CONH—) and linkage containing a silicon atoms which is represented bythe following formula

—Si(R)₂—,

—Si(OR)₂O—,

—OSi(R)₂—, or

—OSi(OR)₂—

wherein R is a hydrocarbon group of 1 to 10 carbon atoms, preferably analkyl group such as methyl or ethyl). A linkage containing two or moreof the above linkages is also available.

Examples of the structures wherein the above-mentioned substituted orunsubstituted hydrocarbon group is bonded to a ring structure throughthe above linkage include an alkoxy group, an acyl group, analkoxycarbonyl group, an aryloxycarbonyl group, an alkylcarbonyloxygroup, an arylcarbonyloxy group, a triorganosilyl group and atriorganosiloxy group.

Specific examples of the alkoxy groups include methoxy and ethoxy;specific examples of the acyl groups include acetyl and benzoyl;specific examples of the alkoxycarbonyl groups include methoxycarbonyland ethoxycarbonyl; specific examples of the aryloxycarbonyl groupsinclude phenoxycarbonyl, naphthyloxycarbonyl, fluorenyloxycarbonyl andbiphenylyloxycarbonyl; specific examples of the alkylcarbonyloxy groupsinclude acetoxy and propionyloxy; specific examples of thearylcarbonyloxy groups include benzoyloxy; specific examples of thetriorganosilyl groups include trialkylsilyl groups, such astrimethylsilyl and triethylsilyl, and trialkoxysilyl groups, such astrimethoxysilyl and triethoxysilyl; and specific examples of thetriorganosiloxy groups include trialkylsiloxy groups, such astrimethylsiloxy and triethylsiloxy, and trialkoxysiloxy groups, such astrimethoxysiloxy and triethoxysiloxy.

Examples of the polar groups include a hydroxyl group, a cyano group, anamide group, an imide group (═NH), an amino group such as a primaryamino group (—NH₂), a sulfonic acid group (—SO₃H), a sulfino group(—SO₂H) and a carboxyl group (—COOH).

<Specific Monomer>

Examples of the specific monomers for use in the invention include:

-   bicyclo[2.2.1]hept-2-ene,-   5-methyl-bicyclo[2.2.1]hept-2-ene,-   5, -dimethyl-bicyclo[2.2.1]hept-2-ene,-   5,6-dimethyl-bicyclo[2.2.1]hept-2-ene,-   5-ethyl-bicyclo[2.2.1]hept-2-ene,-   5-cyclohexylbicyclo[2.2.1]hept-2-ene,-   5-phenyl-bicyclo[2.2.1]hept-2-ene,-   5-(2-naphthyl)-3-bicyclo[2.2.1]hept-2-ene,-   5-vinyl-bicyclo[2.2.1]hept-2-ene,-   5-methoxycarbonyl-bicyclo[2.2.1]hept-2-ene,-   5-phenoxycarbonyl-bicyclo[2.2.1]hept-2-ene,-   5-methoxycarbonylethyl-bicyclo[2.2.1]hept-2-ene,-   5-ethyl-5-methoxycarbonyl-bicyclo[2.2.1]hept-2-ene,-   5-ethyl-5-phenoxycarbonyl-bicyclo[2.2.1]hept-2-ene,-   5-cyano-bicyclo[2.2.1]hept-2-ene,-   5-fluoro-bicyclo[2.2.1]hept-2-ene,-   5,5-difluoro-bicyclo[2.2.1]hept-2-ene,-   5,6-difluoro-bicyclo[2.2.1]hept-2-ene,-   5-chloro-bicyclo[2.2.1]hept-2-ene,-   5,5-dichloro-bicyclo[2.2.1]hept-2-ene,-   5,6-dichloro-bicyclo[2.2.1]hept-2-ene,-   tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   7-methyl-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   8-methyl-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   7-ethyl-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   7-isopropyl-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   7-cyclohexyl-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   7-phenyl-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   7,7-dimethyl-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   7,8-dimethyl-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   7-methyl-8-ethyl-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   7-methoxycarbonyl-tricyclo[4.3.0.1^(2,5)]dec-5-ene,-   8-methoxycarbonyl-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   7-phenoxycarbonyl-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   7-methyl-7-methoxycarbonyl-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   8-methyl-8-methoxycarbonyl-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   7-fluoro-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   8-fluoro-tricycio[4.3.0.1^(2,5)]dec-3-ene,-   7-chloro-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   8-chloro-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   7,7-difluoro-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   7,8-difluoro-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   7,8-dichloro-tricyclo[4.3.0.1^(2,5)]dec-3-ene,-   tetracyclo[4.4 0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-methyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-ethyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-phenyl-tetracyclo[4.4.0.1^(2,5)1^(7,10)]dodec-3-ene,-   8-methoxycarbonyl-tetracyclo[4.4.0.1^(2,5),1^(7,10)]dodec-3-ene,-   8-ethoxycarbonyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-n-propoxycarbonyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-isopropoxycarbonyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-n-butoxycarbonyl-tetracyclo[4.4 0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-phenoxycarbonyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-methyl-8-methoxycarbonyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-methyl-8-ethoxycarbonyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-methyl-8-n-propoxycarbonyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-methyl-8-isopropoxycarbonyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-methyl-8-n-butoxycarbonyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-methyl-8-phenoxycarbonyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-methyl-8-phenyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-fluoro-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8,8-difluoro-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8,8-difluoro-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8,8-dichloro-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8,8-dichloro-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-fluoromethyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-difluoromethyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]-3-ene-   8-trifluoromethyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8,8-bis(trifluoro    ethyl)-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8,9-bis(trifluoromethyl)-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   8-methyl-8-trifluoromethyl-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodec-3-ene,-   pentacyclo[7.4.0.1^(2,5).1^(9,12).0^(8,13)]-3-pentadecene,-   1-methylbicyclo[2.2.1]hept-2-ene,-   7-methylbicyclo[2.2.1]hept-2-ene,-   5-ethoxycarbonylbicyclo[2.2.1]hept-2-ene,-   5-methyl-5-ethoxycarbonylbicyclo[2.2.1]hept-2-ene,-   5-n-butylbicyclo[2.2.1]hept-2-ene,-   5-n-hexylbicyclo[2.2.1]hept-2-ene,-   5-(3-cyclohexenyl)bicyclo[2.2.1]hept-2-ene,-   5-n-octylbicyclo[2.2.1]hept-2-ene,-   5-n-decylbicyclo[2.2.1]hept-2-ene,-   5-isopropylbicyclo[2.2.1]hept-2-ene,-   5-phenyl-1-methylbicyclo[2.2.1]hept-2-ene,-   5-(1-naphthyl)bicyclo[2.2.1]hept-2-ene,-   5-(1-naphthyl)-5-methylbicyclo[2.2.1]hept-2-ene,-   5-(2-naphthyl)-5-methylbicyclo[2.2.1]hept-2-ene,-   5-(biphenyl-4-yl)bicyclo[2.2.1]hept-2-ene,-   5-(biphenyl-4-yl)-5-methylbicyclo[2.2.1]hept-2-ene,-   5-aminomethylbicyclo[2.2.1]hept-2-ene,-   5-trimethoxysilylbicycio[2.2.1]hept-2-ene,-   5-triethoxysilylbicyclo[2.2.1]hept-2-ene,-   5-tri-n-propoxysilylbicyclo[2.2.1]hept-2-ene,-   5-tri-n-butoxysilylbicyclo[2.2.1]hept-2-ene,-   5-hydroxymethylbicyclo[2.2.1]hept-2-ene,-   2,10-dimethyltetracyclo[4.4.0.1^(2,5).1^(7,10)]-3-d decene,-   2,9-dimethyltetracyclo[4.4.0.1^(2,5).1^(7,10)]-3-dodecene,-   pentacyclo[6.5.1.1^(3,6).0^(2,7).0^(9,13)]-4-pentadecene,-   8-ethylidenetetracyclo[4.4.0.1^(2,5).1^(7,10)]-3-dodecene,-   5-chloromethylbicyclo[2.2.1]hept-2-ene,-   5-fluoromethylbicyclo[2.2.1]hept-2-ene,-   5-trifluoromethylbicyclo[2.2.1]hept-2-ene,-   5,5-bis(trifluoromethyl)bicyclo[2.2.1]hept-2-ene,-   5,6-bis(trifluoromethyl)bicyclo[2.2.1]hept-2-ene,-   5-(1-naphthoxy)carbonylbicyclo[2.2.1]hept-2-ene,-   5-(2-naphthoxy)carbonylbicyclo[2.2.1]hept-2-ene,-   5-(4-phenylphenoxy)carbonylbicyclo[2.2.1]hept-2-ene,-   5-methyl-5-(1-naphthoxy)carbonylbicyclo[2.2.1]hept-2-ene,-   5-methyl-5-(2-naphthoxy)carbonylbicyclo[2.2.1]hept-2-ene, and-   5-methyl-5-(4-phenylphenoxy)carbonylbicyclo[2.2.1]hept-2-ene.

However, the present invention is not limited to the above examples.

Of the above specific monomers, the specific monomer wherein at leastone of R¹ to R⁴ in the formula (2) is a specific polar group representedby the following formula (4) is preferably employed from the viewpointthat a cycloolefin-based polymer (A) exhibiting excellent compatibilitywith the vinyl-based polymer (B) is obtained

—(CH₂)_(n)COOR⁸  (4)

wherein n is usually 0 or an integer of 1 to 5, and R⁸ is a hydrocarbongroup of 1 to 15 carbon atoms.

The value of n and the number of carbon atoms of R⁸ in the formula (4)are preferably as small as possible, because as the value of n becomessmaller or the number of carbon atoms of R⁸ becomes smaller, theresulting thermoplastic resin composition has a higher glass transitiontemperature and is more improved in the heat resistance. That is to saysalthough n is usually 0 or an integer of 1 to 5, it is preferably 0 or1, and although is usually a hydrocarbon group of 1 to 15 carbon atoms,it is preferably an alkyl group of 1 to 3 carbon atoms.

Further, the specific monomer of the formula (2) wherein an alkyl groupis further bonded to a carbon atom to which a polar group represented bythe formula (4) is bonded is preferable from the viewpoint that theresulting thermoplastic resin composition and optical film keep goodbalance between the heat resistance and the moisture (water) resistance.The number of carbon atoms of this alkyl group is preferably 1 to 5 morepreferably 1 to 2, particularly preferably 1.

Of such specific monomers8-methyl-8-methoxycarbonyltetra[4.4.0.1^(2,5).1^(7,10)]-3-dodecene and5-methyl-5-methoxycarbonyl-bicyclo[2.2.1]hept-2-ene are preferable fromthe viewpoint that the resulting thermoplastic resin composition andoptical film have excellent heat resistance and a cycloolefin-basedpolymer (A) exhibiting excellent compatibility with the vinyl-basedpolymer (B) is obtained.

DCP-Based Monomer>

Examples of the DCP-based monomers represented by the formula (3) foruse in the invention include:

-   tricyclo[4.3.0.1^(2,5)]deca-3,7-diene,-   7-methyl-tricyclo[4.3.0.1^(2,5)]deca-3,7-diene,-   8-methyl-tricyclo[4.3.0.1^(2,5)]deca-3,7-diene,-   9-methyl-tricyclo[4.3.0.1^(2,5)]deca-3,7-diene,-   7,8-dimethyl-tricyclo[4.3.0.1^(2,5)]deca-3,7-diene,-   7-ethyl-tricyclo[4.3.0.1^(2,5)]deca-3,7-diene,-   7-cyclohexyl-tricyclo[4.3.0.1^(2,5)]deca-3,7-diene,-   7-phenyl-tricyclo[4.3.0.1^(2,5)]deca-3,7-diene,-   7-(4-biphenyl)-tricyclo[4.3.0.1^(2,5)]deca-3,7-diene,-   7-methoxycarbonyl-tricyclo[4.3.0.1^(2,5)]deca-3,7-diene,-   7-phenoxycarbonyl-tricyclo[4.3.0.1^(2,5)]deca-3,7-diene,-   7-methyl-7-methoxycarbonyl-tricyclo[4.3.0.1^(2,5)]deca-3,7-diene,-   7-fluoro-tricyclo[4.3.0.1^(2,5)]deca-3,7-diene,-   7,8-difluoro-tricyclo[4.3.0.1^(2,5)]deca-3,7-diene, and-   7-chloro-tricyclo[4.3.0.1^(2,5)]deca-3,7-diene.

However, the present invention is not limited to the above examples.

<Copolymerizable Monomer>

The specific monomer and the DCP-based monomer may be each independentlyring-opening polymerized, or the specific monomer and the DCP-basedmonomer may be ring-opening copolymerized, or the specific monomerand/or the DCP-based monomer and another copolymerizable monomer may bering-opening copolymerized.

Examples of the copolymerizable monomers include cycloolefins, such ascyclobutene, cyclopentene, cycloheptene, cyclooctene and5-ethylidene-2-norbornene. The number of carbon atoms of eachcycloolefin is in the range of preferably 4 to 20, more preferably 5 to12. The specific monomer and/or the DCP-based monomer may bering-opening polymerized in the presence of an unsaturatedhydrocarbon-based polymer containing a carbon-carbon double bond in themain chain, such as polybutadiene, polyisoprene, a styrene/butadienecopolymer, an ethylene/non-conjugated diene copolymer or a ring-openedmetathesis (co)polymer of a norbornene derivative. In this case, theresulting ring-opened copolymer and its hydrogenated copolymer areuseful as raw materials of a thermoplastic resin composition having highimpact resistance.

<Ring-Opening Polymerization Catalyst>

As a catalyst for use in the ring-opening (co)polymerization (alsoreferred to as a “ring-opening polymerization catalyst” hereinafter), ametathesis catalyst can be mentioned. This metathesis catalyst is acatalyst comprising a combination of:

(a) at least one compound selected from a tungsten-containing compound,a molybdenum-containing compound and a rhenium-containing compound, and

(b) at least one compound selected from compounds containing Group IAelements (e.g., Li, Na, K), Group IIA elements (e.g., Mg, Ca), GroupIIIB elements (e.g., Zn, Cd, Hg), Group IIIB elements (e.g., B, Al),Group IVA elements (e.g., Ti, Zr) or Group IVB elements (e.g., Si, Sn,Pb) of Deming's periodic table and having at least one saidelement-carbon bond or at least one said element-hydrogen bond.

Examples of the compounds (a) include compounds described in JapanesePatent Laid-Open Publication No, 240517/1989, such as WCl₆, MoCl₆ andReOCl₃.

Examples of the compounds (b) include compounds described in JapanesePatent Laid-Open Publication No. 2405117/989, such as n-C₄H₉Li ,(C₂H₅)₃Al, (C₂H₅)₂AlCl, (C₂H₅)_(1.5)AlCl_(1.5), (C₂H₅)AlCl₂,methylalumoxane and LiH.

In the present invention, in order to enhance activity of thering-opening polymerization catalyst, alcohols, aldehydes, ketones,amines and compounds described in Japanese Patent Laid-Open PublicationNo. 240517/1989 can be added as additives (c).

The metathesis catalyst is used in such an amount that the molar ratiobetween the amount of the compound (a) and the total amount of thespecific monomer and the DCP-based monomer (compound (a):specificmonomer and DCP-based monomer) becomes usually 1:500 to 1.100000,preferably 1:1000 to 1:50000. The ratio between the compound (a) and thecompound (b) ((a):(b)) is in the range of usually 1:1 to 1:50,preferably 1:2 to 1:30, in terms of a metal atom ratio. The ratiobetween the additive (c) and the compound (a, ((c):(a)) is in the rangeof usually 0.005:1 to 15:1, preferably 0.05:1 to 7:1, in terms of amolar ratio.

<Molecular Weight Modifier>

The molecular weight of the ring-opened (copolymer can be controlled bypolymerization temperature, type of a catalyst and type of a solvent,but in the present invention, control of the molecular weight ispreferably carried out by allowing a molecular weight modifier tocoexist in the reaction system. Examples of the molecular weightmodifiers include c-olefins, such as ethylene, propene, 1-butene,1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene and 1-decene; andvinyl aromatic compounds, such as styrene, 4-vinylbiphenyl,1-vinylnaphthalene and 2-vinylnaphthalene. Of these, 1-butene and1-hexene are particularly preferable. These molecular weight modifierscan be used singly or as a mixture of two or more kinds. The molecularweight modifier is used in an amount of usually 0.005 to 0.6 mol.preferably 0.02 to 0.5 mol. based on 1 mol of the total amount of thespecific monomer and the DCP-based monomer used in the ring-opening(co)polymerization.

<Ring-Opening Polymerization Solvent>

In the ring-opening (copolymerization, a solvent is preferably used inorder to dissolve the specific monomer, the DCP-based monomer, thering-opening polymerization catalyst and the molecular weight modifier.Examples of the solvents for use in the ring-opening (co)polymerizationinclude alkanes, such as pentane, hexane, heptane, octane, nonane anddecane; cycloalkanes, such as cyclohexane, cycloheptane, cyclooctane,decalin and norbornane; aromatic hydrocarbons, such as benzene, toluene,xylene, ethybenzene and cumene; halogenated alkanes, such aschlorobutane, bromohexane, methylene chloride, dichloroethane,hexamethylene dibromide, chloroform and tetrachloroethylene; halogenatedaryls, such as chlorobenzene; saturated carboxylic esters, such as ethylacetate, n-butyl acetate, isobutyl acetate and methyl propionate; andethers, such as dibutyl ether, tetrahydrofuran and dimethoxyethane.These solvents can be used singly or as a mixture of two or more kinds.Of these, aromatic hydrocarbons are preferable. The solvent is used insuch an amount that the weight ratio between the amount of the solventand the total amount of the specific monomer and the DCP-based monomer(solvent:specific monomer and DCP-based monomer) becomes usually 1:1 to10:1, preferably 1:1 to 5:1.

<Ring-Opening (co)Polymerization Reaction>

The ring-opened (co)polymer can be obtained by ring-opening(co)polymerizing the specific monomer and/or the DCP-based monomer, andif necessary, the copolymerizable monomer in the presence of aring-opening polymerization catalyst and using if necessary a molecularweight modifier and a ring-opening polymerization solvent.

In case of copolymerization of the specific monomer and the DCP-basedmonomer, it is desirable that the specific monomer in an amount ofusually 50 to 99% by weight, preferably 60 to 95% by weight, morepreferably 70 to 95% by weight, and the DCP-based monomer in an amountof usually 1 to 50% by weight, preferably 5 to 40% by weight, morepreferably 5 to 30% by weight, based on the total 100% by weight of thespecific monomer and the DCP-based monomer, are copolymerized.

In case of copolymerization of the specific monomer and/or the DCP-basedmonomer and the copolymerizable monomer, it is desirable that thespecific monomer in an amount of usually not less than 50% by weight andless than 100% by weight, preferably not less than 60% by weight andless than 100% by weight, more preferably not less than 70% by weightand less than 100% by weight, the DCP-based monomer in an amount ofusually 0 to 50% by weight, preferably 0 to 40% by weight, morepreferably 0 to 30% by weight, and the copolymerizable monomer in anamount of usually more than 0% by weight and not more than 50% byweight, preferably more than 0% by weight and not more than 40% byweight, more preferably more than 0% by weight and not more than 30% byweight, based on the total 100% by weight of the specific monomers theDCP-based monomer and the copolymerizable monomer, are copolymerized.

As the ring-opened (co)polymer for use in the invention, a homopolymerof the specific monomer or a copolymer of two or more of the specificmonomers is most preferable.

<Hydrogenation Reaction>

Although the ring-opened (copolymer obtained by the ring-opening(co)polymerization reaction can be used as it is as thecycloolefin-based polymer (A), this ring-opened (co)polymer has anolefinic unsaturated bond in a molecule, and a problem of heat tintingor the like sometimes takes place. On this account, it is preferable touse a hydrogenated (co)polymer obtained by hydrogenating the olefinicunsaturated bond.

This hydrogenation reaction can be carried out by, for example, adding ahydrogenation catalyst to a solution of the ring-opened (co)polymer andallowing a hydrogen gas of atmospheric pressure to 30 MPa, preferably 3to 20 MPa, to act thereon at 0 to 200° C., preferably 20 to 180° C.

As the hydrogenation catalyst, a catalyst that is used for usualhydrogenation reaction of an olefinic compound, such as a publicly knownheterogeneous or homogeneous catalyst, is employable. Examples of theheterogeneous catalysts include solid catalysts wherein precious metalcatalytic substances, such as palladium, platinum, nickel, rhodium andruthenium, are supported on carriers such as carbon, silica, alumina andtitanic. Examples of the homogeneous catalysts include nickelnaphthenate/triethylaluminum, nickel acetylacetonate/triethylaluminum,cobalt octenate/n-butyllithium, titanocene dichloride/diethylaluminummonochloride, rhodium acetate, chlorotris(triphenylphosphine)rhodium,dlchlorotris(triphenylphosphine)ruthenium,chlorohydrocarbonyltris(triphenylphosphine)ruthenium anddichlorocarbonyltris(triphenylphosphine)ruthenium. Such catalysts may bein the form of a power or particles. The hydrogenation catalyst is usedin such an amount that the ratio between the ring-opened (copolymer andthe hydrogenation catalyst (ring-opened (co)polymer:catalyst) becomesusually 1:1×10⁻⁶ to 1:2 (by weight).

The degree of hydrogenation of the olefinic unsaturated bonds is usuallynot less than 50%, preferably not less than 70%, more preferably notless than 90%.

By hydrogenating the ring-opened (co)polymer in the above manner, theresulting hydrogenated (co)polymer has excellent heat stability, anddeterioration of properties of the (O)polymer caused by heating in themolding process or in the use of the manufactured article can beprevented

<Saturated Copolymer>

In the present invention in addition to the ring-opened (co)polymer anda hydrogenated (co)polymer thereof, a saturated copolymer of thespecific monomer and an unsaturated double bond-containing compound canbe also employed as the cycloolefln-based polymer (A). It is desirablethat the specific monomer in an amount of usually 0 to 90% by weight,preferably 70 to 90% by weight, more preferably 80 to 90% by weight, andthe unsaturated double bond-containing compound in an amount of usually10 to 40% by weight, preferably 10 to 30% by weight, more preferably 10to 20% by weight, based on the total 100% by weight of the specificmonomer and the unsaturated double bond-containing compound, arecopolymerized.

Examples of the unsaturated double bond-containing compounds includeolefin-based compounds of 2 to 12 carbon atoms, preferably 2 to 8 carbonatoms, such as ethylene, propylene and butene.

As a catalyst for use in the copolymerization reaction of the specificmonomer with the unsaturated double bond-containing compound, a catalystcomprising a vanadium compound and an organoaluminum compound can bementioned. The vanadium compound is, for examples a vanadium compoundrepresented by the formula VO(OR)_(a)X_(b) or V(OR)_(c)X_(d) (wherein Ris a hydrocarbon group, 0≦a≦3, 0≦b≦3, 2≦a+b≦3, 0≦c≦4, 0≦d≦4 and 3≦c+d≦4)or an electron donor adduct thereof. Examples of the electron donorsinclude oxygen-containing electron donors, such as alcohols phenols,ketone, aldehyde, carboxylic acid, ester of organic acid or inorganicacid, ethers acid amide, acid anhydride and alkoxysilane; andnitrogen-containing electron donors, such as ammonia, amine, nitrile andisocyanate. The organoaluminum compound is, for examples at least oneorganoaluminum compound selected from compounds having at least onealuminum-carbon bond or aluminum-hydrogen bond. The proportion of theorganoaluminum compound to the vanadium compound in the catalyst is asfollows. That is to say, the ratio of the aluminum atom to the vanadiumatom (Al/V) is usually not less than 2, preferably 2 to 50, particularlypreferably 3 to 20.

Examples of solvents employable in the above copolymerization reactioninclude alkanes, such as pentane, hexane, heptane, octane, nonane anddecane; cycloalkanes, such as cyclohexane and methylcyclohexane; andaromatic hydrocarbons, such as benzene, toluene and xylene, and theirhalogen derivatives. Of these, cyclohexane is preferable.

<Cycloolefin-Based Polymer (A)>

The cycloolefln-based polymer (A) for use in the invention has anintrinsic viscosity [η], as measured in a chlorobenzene solution(concentration: 0.5 g/100 ml) at 30° C., of 0.2 to 5.0 dl/g, preferably0.3 to 4.0 dl/g, particularly preferably 0.35 to 1.5 dl/g. Further, thepolymer (A) desirably has a number-average molecular weight (Mn) interms of polystyrene, as measured by gel permeation chromatography(GPC), of usually 8,000 to 1,00,000, preferably 10,000 to 500,000, morepreferably 20,000 to 100,000, and a weight-average molecular weight (Mw)of usually 10,000 to 3,000,000, preferably 20,000 to 1,000,000, morepreferably 30,000 to 500,000.

If the molecular weight is too low, strength of the resulting moldedarticle or film sometimes becomes low. If the molecular weight is toohigh, the solution viscosity becomes too high, and productivity orprocessability of the thermoplastic resin composition of the inventionis sometimes deteriorated.

The cycloolefin-based polymer (A) desirably has a molecular weightdistribution (Mw/Mn) of usually 1.5 to 10, preferably 2 to 8, morepreferably 2.2 to 5.

The cycloolefin-based polymer (A) has a glass transition temperature(Tg) of usually 110 to 250° C., preferably 115 to 220° C., morepreferably 120 to 200° C. If Tg is too low, the heat distortiontemperature is lowered, so that a problem of heat resistance is liableto occur, and besides, there sometimes occurs a problem that change inoptical properties of the resulting molded article or film withtemperature becomes large. On the other hand, if Tg is too nigh, theprocessing temperature needs to be raised, and thereby, thethermoplastic resin composition sometimes suffers heat deterioration.

(B) Vinyl-Based Polymer

The vinyl-based polymer (B) for use in the invention is a polymer havinga structural unit derived from p-isopropenylphenol and is preferably acopolymer further having a structural unit derived from a vinyl-basedmonomer (b) other then p-isopropenylphenol. Such a vinyl-based polymer(B) can be obtained by copolymerizing p-isopropenylphenol and avinyl-based monomer (b).

Because the vinyl-based polymer (B) contains a structural unit derivedfrom p-isopropenylphenol, the resulting thermoplastic resin compositionand optical film have excellent compatibility and is enhanced inweathering resistance and heat resistance.

<Vinyl-Based Monomer (b)>

The vinyl-based monomer (b) is, for example, an aromatic vinyl-basedmonomer, a vinyl cyanide-based monomer, an acrylate-based monomer, amethacrylate-based monomer, a maleic anhydride monomer or a maleimidemonomer. Of these, an aromatic vinyl-based monomer or a vinylcyanide-based monomer is preferably employed, and a combination or anaromatic vinyl-based monomer and a vinyl cyan-de-based monomer isparticularly preferably employed.

Examples of the aromatic vinyl-based monomers include styrene; alkylsubstituted styrenes such as α-methylstyrene, β-methylstyrene andp-methylstyrene; halogen substituted styrenes, such as 4-chlorostyreneand 4-bromostyrene; hydroxystyrenes, such as p-hydroxystyrene,2-methyl-4-hydroxystyrene and 3,4-dihydroxystyrene; vinylbenzylalcohols; alkoxy substituted styrenes, such as p-methoxystyrene,p-t-butoxystyrene and m-t-butoxystyrene; vinylbenzoic acids, such as3-vinylbenzoic acid and 4-vinylbenzoic acid; 2-phenylacrylic acid;vinylbenzoic esters, such as methyl 4-vinylbenzoate and ethyl4-vinylbenzoate; 4-vinylbenzyl acetate; 4-acetoxystyrene;vinylacetophenones, such as p-butenylacetophenone andm-isopropenylacetophenone; amidostyrenes, such as 2-butylamidostyrene,4-methylamidostyrene and p-sulfonamidostyrene; aminostyrenes, such as3-aminostyrene, 4-aminostyrene, 2-isopropenylaniline andvlnylbenzyldimethylamirne; nitrostyrenes, such as 3-nitrostyrene and4-nitrostyrene; cyanostyrenes, such as 3-cyanostyrene and4-cyanostyrene; vinylphenylacetonrtrile; arylstyrenes, such asphenylstyrene; vinylnaphthalene; vinylanthracene; and1,1-diphenylethylene. Of theses styrene and α-methylstyrene arepreferable from the viewpoints of ease of industrial obtaining and lowcost.

Further, the vinyl cyanide-based monomer is preferably used because acopolymer of high molecular weight is obtained, and examples thereofinclude acrylonitrile and methacrylonitrile.

Examples of the acrylate-based monomers include alkyl acrylates, such asmethyl acrylate and ethyl acrylate; benzyl acrylate; phenyl acrylate;and hydroxyalkyl acrylates, such as 2-hydroxyethyl acrylate and3-hydroxypropyl acrylate.

Examples of the methacrylate-based monomers include alkyl methacrylates,such as methyl methacrylate and ethyl methacrylate; benzylmethyacrylate; phenyl methacrylate; and hydroxyalkyl methacrylates, suchas 2-hydroxyethyl methacrylate and 3-hydroxypropyl methacrylate.

<Radical Polymerization Initiator>

When the vinyl-based polymer (B) for use in the invention is synthesizedby radical polymerization, a publicly known organic peroxide thatgenerates free radical or an azobis radical polymerization initiator canbe employed.

Examples of the organic peroxides include

diacyl peroxides, such as diacetyl peroxide, dibenzoyl peroxide,diisobutyroyl peroxide, di(2,4-dichlorobenzoyl)peroxide,di(3,5,5-tri-methylhexanoyl)peroxide, dioctanoyl peroxide, dilauroylperoxide, distearoyl peroxide and bis{4-(m-toluoyl)benzoyl}peroxide;

ketone peroxides, such as methyl ethyl ketone peroxide, cyclohexanoneperoxide, methylcyclohexanone peroxide and acetylacetone peroxide;

hydroperoxides, such as hydrogen peroxide, t-butyl hydroperoxide,-cumene hydroperoxide, p-menthane hydroperoxide, diisopropylbenzenehydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide and t-hexylhydroperoxide;

dialkyl peroxides, such as di-t-butyl peroxide, dicumyl peroxide,dilauryl peroxide, α,α′-bis(t-butylperoxy)diisopropylbenzene,2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, t-butylcumyl peroxide and2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3;

peroxy esters, such as t-butyl peroxyacetate, t-butyl peroxypivalate,t-hexyl peroxypivalate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate,2,5-dimethyl-1-bis(2-ethylhexanoylperoxy)hexane,1-cyclohexyl-1-methylethyl peroxy-2-ethylhexanoate, t-hexylperoxy-2-ethylhexanoate, t-butyl peroxy-2-ethylhexanoate, t-butylperoxyisobutyrate, t-butyl peroxymaleate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butyl peroxylaurate,2,5-dimethyl-2,5-bis(m-toluoylperoxy)hexane,α,α′-bis(neodecanoylperoxy)diisopropylbenzene, cumyl peroxyneodecanoate,1,1,3,3-tetramethylbutyl peroxyneodecanoate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, t-hexyl peroxyneodecanoate, t-butylperoxyneododecanoate, t-butyl peroxybenzoate, t-hexyl peroxybenzoate,bis(t-butylperoxy)isophthalate,2,5-dimethyl-2,5-bis(benzoylperoxy)hexane, t-butylperoxy-m-toluoylbenzoate and3,3′,4,4′-tetra(t-butylperoxycarbonyl)benzophenone;

peroxy ketals, such as1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(t-hexylperoxy)cyclohexane,1,1-bis(t-butylperoxy)-3,-3,5-trimethylcyclohexane,1,1-bis(t-butylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)cyclododecane,2,2-bis(t-butylperoxy)butane, n-butyl 4 4-bis(t-butylperoxy)pivalate and2 2-bis(4,4-di-t-butylperoxycyclohexylpropane;

peroxy monocarbonates, such as t-hexyl peroxyisopropyl monocarbonate,t-butyl peroxyisopropyl monocarbonate, t-butyl peroxy-2-ethylhexylmonocarbonate and t-butyl peroxyallyl monocarbonate;

peroxy dicarbonates, such as di-sec-butyl peroxydicarbonate, di-n-propylperoxydicarbonate, diisopropyl peroxydicarbonate,bis(4-t-butylcyclohexyl) peroxydicarbonate, di-2-ethoxyethylperoxydicarbonate, di-2-ethylhexyl peroxydicarbonate, di-2-methoxybutylperoxydicarbonate and di(3-methyl-3-methoxybutyl) peroxydicarbonate; and

other compounds, such as t-butyltrimethylsilyl peroxide.

However, the organic peroxide employable in the invention is not limitedto the above-exemplified compounds.

Of the above organic peroxides, polyfunctional peroxy ketals arepreferable because a (copolymer of high molecular weight can be easilyobtained. In particular, tetrafunctional2,2-bis(4,4-di-t-butylperoxycyclohexyl) propane is preferable.

Examples of the azobis radical polymerization initiators include2,2′-azobisisobutyronitrile, azobisisovaleronitrile,2,2′-azobis(4-methoxy-2,4-dimethylvaleronitriloe),2,2′-azobis(2,4-dimethylvaleronitrile,2,2′-azobis(2-methylbutyronitrile),1,1′-azobis(cyclohexane-1-carbonitrile),2-(carbamoylazo)isobutyronitrile,2,21-azobis[2-methyl-N-{1,1′-bis(hydroxymethyl)-2-hydroxyethyl}propionamide],2,2′-azobis[2-methyl-N-{2-1-hydroxybutyl}propionamide],2,2′-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide],2,2′-azobis[N-(2-propenyl)-2-methylpropionamide],2,2′-azobis(N-butyl-2-methylpropionamide),2,2′-azobis(N-cyclohexyl-2-methylpropionamide),2,2′-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride,2,2′-azobis[2-(2-imidazolin-2-yl)propane]disulfate•dihydrate,2,2′-azobis[2-(3,4,5,6-tetrahydropyrimidin-2-yl)propane]dihydrochloride,2,2′-azobis[2-{1-(2-hydroxyethyl)-2-imidazolin-2-yl}propane]dihydrochloride,2,2′-azobis[2-(2-imidazolin-2-yl)propane],2,2′-azobis(2-methylpropionamidine)dihydrochloride,2,2′-azobis[N-(carboxyethyl)-2-methyl-propionamidine],2,2′-azobis(2-methylpropionamidoxime), dimethyl 2,2′-azobisbutyrate,4,4′-azobis(4-cyanopentanoic acid) and2,2′-azobis(2,4,4-trimethylpentane). However, the azobis radicalpolymerization initiator employable -in the invention is not limited tothe above-exemplified compounds.

<Catalysts>

In the copolymerization reaction of p-isopropenylphenol with thevinyl-based monomer (b) a catalyst may be employed. This catalyst is notspecifically restricted, and for example, an anionic polymerizationcatalyst, a coordination anionic polymerization catalyst and a cationicpolymerization catalyst which are publicly known are employable.

<Vinyl-Based Polymer (B)>

The vinyl-based polymer (B) for use in the invention is obtained bycopolymerizing p-isopropenylphenol and the vinyl-based monomer (b) inthe presence of the polymerization initiator and the catalyst by apublicly known process, such as bulk polymerization, solutionpolymerization, precipitation polymerization, emulsion polymerization,suspension polymerization or bulk-suspension polymerization.

It is desirable that in the vinyl-based polymer (B) obtained as above,the structural units derived from p-isopropenylphenol are contained inamounts of usually 0.5 to 30% by weight, preferably 1.5 to 15% byweight, more preferably 1.5 to 10% by weight, and the structural unitsderived from the vinyl-based monomer (b) are contained ,in amounts ofusually 70 to 99.5% by weight preferably 85 to 98.5% by weight, morepreferably 90 to 98.5% by weight, based on the total 100% by weight ofthe structural units derived from p-isopropenylphenol and the structuralunits derived from the vinyl-based monomer (b). When the proportion ofthe structural units derived from p-isopropenylphenol is in the aboverange, the cycloolefin-based polymer (A) and the vinyl-based polymer (B)are well compatibilized, and the resulting thermoplastic resincomposition and optical film exhibit excellent property of lowbirefringence and is enhanced in the weathering resistance and the heatresistance. Especially in case of a copolymer of p-isopropenylphenol andan aromatic vinyl monomer, it is desirable that the structural unitsderived from p-isopropenylphenol are contained in amounts of usually 0.5to 30% by weight preferably 1.5 to 15% by weight, more preferably 1.5 to10% by weights and the structural units derived from the aromatic vinylmonomer (b) are contained in amounts of usually 70 to 99.5% by weightpreferably 85 to 98.5% by weight, more preferably 90 to 98.5% by weightsbased on the total 100% by weight of the structural units derived fromp-isopropenylphenol and the structural units derived from the aromaticvinyl monomer.

In the case where the vinyl-based polymer (B) contains a structural unitderived from a vinyl cyanide monomer, it is desirable that thestructural units derived from p-isopropenylphenol are contained inamounts of usually 0.5 to 30% by weight, preferably 1.5 to 15% byweight, more preferably 1.5 to 10% by weights the structural unitsderived from the vinyl cyanide monomer are contained in amounts ofusually 0.5 to 20% by weight, preferably 1 to 10% by weight, morepreferably 3 to 6% by weight, and the structural units derived from thevinyl-based monomer (b), preferably structural units derived from thearomatic vinyl-based monomer (b), are contained in the residual amount,i.e., usually 50 to 99% by weights preferably 75 to 97.5% by weight,more preferably 84 to 99.5% by weights based on 100% by weight of allthe structural units of the vinyl-based polymer (B). If the amounts ofthe structural units derived from the vinyl cyanide monomer exceed 20%by weight, compositional distribution is produced between the copolymerprepared in the initial stage of the polymerization and the copolymerprepared in the latter stage of the polymerization, and therefore, atransparent copolymer is not obtained occasionally.

The vinyl-based polymer (B) desirably has a number-average molecularweight (Mn) in terms of polystyrene, as measured by gel permeationchromatography (GPC), of usually 3,000 to 350,000, preferably 10,000 to175,300, more preferably 10,000 to 90,000, and a weight-averagemolecular weight (Mw) of usually 500 to 500,000, preferably 5,000 to250,000, more preferably 20,000 to 100,000.

If the molecular weight is too low, strength of the resulting moldedarticle or film sometimes becomes low. If the molecular weight is toohigh, the solution viscosity becomes too high, and productivity orprocessability of the thermoplastic resin composition of the inventionis sometimes deteriorated.

The vinyl-based polymer (B) desirably has a molecular weightdistribution (Mw/Mn) of usually 1.0 to 10, preferably 1.2 to 5, morepreferably 1.2 to 4.

<Thermoplastic Resin Composition and Optical Film>

In the thermoplastic resin composition and the optical film of theinvention, the cycloolefin-based polymer (A) and the vinyl-based polymer(B) are contained in he following proportions. That is to say, based on100 parts by weight of the cycloolefin-based polymer (A), thevinyl-based polymer (B) is contained in an amount of usually 0.01 to 300parts by weight, preferably 10 to 300 parts by weight, more preferably40 to 150 parts by weight. When the amount of the vinyl-based polymer(B) is in the above ranges a thermoplastic resin composition and anoptical film both of which exhibit property of low birefringence andhave excellent weathering resistance and heat resistance can beobtained. Further, strength of a molded article such as a film can beenhanced. If the amount of the vinyl-based polymer (B) is less than thelower limit of the above range, the value of birefringence of theresulting thermoplastic resin composition or optical film is notsufficiently decreased occasionally. If the amount of the vinyl-basedpolymer (B) exceeds the upper limit of the above range, heat resistanceof the resulting thermoplastic resin composition or optical film issometimes lowered, and transparency of the optical film sometimeslowered.

In the case where a retardation film is formed from such an opticalfilm, a thermoplastic resin composition containing the vinyl-basedpolymer (B) in an amount of preferably 10 to 100 parts by weight, morepreferably 15 to 75 parts by weight, particularly preferably 20 to 65parts by weight, based on 100 parts by weight of the cycloolefin-basedpolymer (A) is desirable. When such a thermoplastic resin composition isused, a retardation film exhibiting excellent appearance of retardationand having excellent wavelength dispersion properties can be obtained.

On the other hand, in the case where the thermoplastic resin compositionis applied to an injection molded article, the vinyl-based polymer (B)is contained in an amount of preferably 10 to 300 parts by weight, morepreferably 30 to 150 parts by weight, particularly preferably 40 to 100parts by weight, based on 100 parts by weight of the cycloolefin-basedpolymer (A).

The thermoplastic resin composition and the optical film may furthercontain a hydrocarbon resin Examples of the hydrocarbon resins includeC₅-based resins, C₉-based resins, C₅-based/C₉-based mixture resins,cyclopentadiene-based resins, olefin/vinyl substituted aromatic compoundcopolymer-based resins, hydrogenation products of these resins andhydrogenation products of vinyl substituted aromatic resins. The contentof the hydrocarbon resin is in the range of usually 0.01 to 50 parts byweight, preferably 0.1 to 25 parts by weight, based on 100 parts byweight of the cycloolefin-based polymer (A).

In order to improve heat deterioration resistance and light resistance,publicly known phenol-based or hydroquinone-based antioxidants, such as2,6-di-t-butyl-4-methylphenol,2,2′-d-oxy-3,3′-di-t-butyl-5,5′-dimethyldiphenylmethane,tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionato]methane,stearyl-p-(3,5-di-t-butyl-4-hydroxyphenyl) propionate and1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene; andpublicly known phosphorus-based antioxidants, such astris(4-methoxy-3,5-diphenyl) phosphite, tris(nonylphenyl) phosphite andtris(2,4-di-t-butylphenyl) phosphite, can be contained in thethermoplastic resin composition and the optical film. These antioxidantscan be contained singly or in combination of two or more kinds. Further,in order to improve light resistance of the thermoplastic resincomposition and the optical film, publicly known ultraviolet lightabsorbers, such as 2,4-dihydroxybenzophenone,2-hydroxy-4-methoxybenzophenone and2,2′-methylenebis[4-(1,1,3,3,-tetramethylbutyl)-6-[2H-benzotriazol-2-yl]phenol]],may be contained. Moreover, a lubricant to improve processability may beadded, or publicly known additives, such as flame retardant, anti-fungusagent, colorant, release agent and foaming agent, may be added whenneeded. These additives can be used singly or in combination of two ormore kinds.

In the case where the thermoplastic resin composition of the inventionis applied to an injection molded article the stress optical coefficient(C_(R)) is preferably as small as possible, and specifically it ispreferably not more than 1500, particularly preferably not more than500, because birefringence hardly occurs in the molded article.

<Process for Preparing Thermoplastic Resin Composition>

The thermoplastic resin composition of the invention can be prepared by,for example, the following processes:

(i) a process comprising mixing the cycloolefin-based polymer (A), thevinyl-based polymer (B) and arbitrary components by the use of atwin-screw extruder, a roll kneading machine or the like, and

(ii) a process comprising adding the vinyl-based polymer (B) to asolution of the cycloolefin-based polymer (A, in an appropriate solventand mixing them.

<Process for Producing Optical Film>

The optical film of the invention can be produced by, for example,molding the thermoplastic resin composition into a film by a publiclyknown molding method, such as injection molding, compression molding orextrusion molding.

The optical film can be also produced by dissolving or dispersing thecycloolefin-based polymer (A) and the vinyl-based polymer (B) in anappropriate solvent and then casting the resulting solution ordispersion by a solvent casting method to form a film. The solvent usedherein is not specifically restricted provided that it is usually usedfor the solvent casting method and is capable of sufficiently dissolvingthe cycloolefin-based polymer (A) and the vinyl-based polymer (B). Forexample, a polar solvent or a non-polar solvent is employable. The polarsolvent means a solvent having a dielectric constant of not less than 4and less than 80, and the non-polar solvent means a solvent having adielectric constant of not less than 1 and less than 4.

Examples of such polar solvents include water (78.5), dimethyl sulfoxide(46.7), acetonitrile (37.5), N,N-dimethylacetamide (37.8),7-butyrolactone (39.0), dimethylformamide (36.7), methanol (32.6),N-methyl-2-pyrrolidone (32.0), tetramethylurea (23.0) acetone (20.7),1-propanol (20.1), methyl ethyl ketone (18.5), 2-propanol (18.3),1-butanol (17.8), 2-methxyethanol (16.9), 2-butanol (15.8), isobutylalcohol (15.8), 2-ethoxyethanol (13.0), pyridine (12.3),o-dichlorobenzene (9.9), methylene chloride (9.1), tetrahydrofuran(7.6), acetic acid (6.2), ethyl acetate (6.0), chlorobenzene (5.7),chloroform (4.8) and diethyl ether (4.3).

Examples of the non-polar solvents include o-xylene (2.6), toluene(2.4), p-xylene (2.3), benzene (2.3), carbon tetrachloride (2.2),cyclohexane (2.0), cyclopentane (2.0), heptane (1.9), hexane (1.9),nonane (2.0), pentane (1.8), trichloroethylene (3.4) and2,2,4-trimethylpentane (1.9). The numbers in the parentheses are each adielectric constant of each solvent.

The above solvents can be used singly or as a mixture of plural kinds.When a mixture of the solvents is used, the dielectric constant of themixed solvent is desired to be in the range of 2 to 15, preferably 4 to10. In this case, the value of the dielectric constant of the mixedsolvent at 20° C. can be estimated from a mixing ratio (by weightbetween the solvents, and for example, if a solvent a and a solvent bare mixed and if the weight fractions of the solvents a and b are takenas W_(a) and W_(b), respectively, and if the dielectric constants of thesolvent a and b at 20° C. are taken as ∈_(a) and ∈_(b), respectively,the dielectric constant (∈ value) of the mixed solvent can be determinedby the following formula:

∈ value=W _(a)·∈_(a) +W _(b)·∈_(b)

The solvent has a boiling point, at atmospheric pressure, of usually nothigher than 100° C., preferably not higher than 70° C., particularlypreferably not higher than 45° C. If a solvent having a boiling point ofhigher than 100° C. is used, the drying time after film formationbecomes long, and productivity is sometimes deteriorated. Moreover, alarge amount of the solvent remains in the film, and this sometimesdeteriorates optical properties such as appearance of retardation.

Of the above solvents, methylene chloride is particularly preferablyused because it has a low boiling point. if a conventional thermoplasticresin composition comprising a cycloolefin-based polymer and avinyl-based polymer is dissolved in methylene chloride without using acompatibilizing agents then the solution is subjected to film formationand thereafter methylene chloride is evaporated, there occurs a problemthat the resulting film becomes opaque. In case of the thermoplasticresin composition of the inventions however, a transparent film can beobtained even if a compatibilizing agent is not used. As a result,drying at a temperature lower than the temperature of the conventionaldrying becomes possible, and heat deterioration in the film productionprocess can be prevented.

The concentration of the thermoplastic resin composition in the solution(sometimes referred to as a “film-forming solution” hereinafter) used inthe solvent casting method is in the range of usually 0.1 to 70% byweight, preferably 1 to 50% by weight, more preferably 10 to 35% byweight. If the concentration is too low, it becomes difficult to obtaina film having a desired thickness and when the solvent is removed bydrying foaming is liable to take place with evaporation of the solvent,and hence, it sometimes becomes difficult to obtain a film of excellentsurface smoothness. On the other hand, if the concentration is too high,the viscosity of the film-form-ng solution becomes too high, and henceit sometimes becomes difficult to obtain a film or uniform thickness anduniform surface profile.

The viscosity of the film-forming solution at room temperature is in therange of usually 1 to 1,000,000 (mPa·s), preferably 10 to 100,000(mPa·s), more preferably 100 to 80,000 (mPa·s), particularly preferably1,000 to 60,000 (mPa·s).

The temperature in the preparation of the film-forming solution may beroom temperature or higher than room temperature, and it has only to bea temperature at which the cycloolefln-based polymer (A) and thevinyl-based polymer (B) are homogeneously dissolved or dispersed bymixing them sufficiently.

To the film-forming solution, a colorant such as a dye or a pigment canbe properly added when needed, and by the use of the colorant, a coloredfilm can be obtained.

In order to improve surface smoothness of the resulting film, a levelingagent may be added to the film-forming solution. As the leveling agent,any of various agents generally used is employable, and examples of suchleveling agents include fluorine-based nonionic surface active agents,special acrylic resin-based leveling agents and silicon-based levelingagents.

The film-forming solution prepared as above is cast by pouring orapplying the solution onto an appropriate carrier, whereby a layer ofthe film-forming solution is formed on the carrier. As the carrier, ametal drum, a steel belt, a polyester film made of polyethyleneterephthalate (PET) or polyethylene naphthalate (PEN), apolytetrafluoroethylene belt or the like is employable.

If a polyester film is used as a carrier, the polyester film may be asurface-treated film. As a method of surface treatment, there can bementioned a hydrophilic treatment method generally performed, such as amethod of forming a layer of an acrylic resin or a sulfonic acidbase-containing resin on a surface of a polyester film by coating orlaminating or a method of increasing hydrophilicity of a film surface bycorona discharge treatment or the like.

When a metal drum, a steel belt, a polyester film or the like whosesurface has been subjected to sand matting treatment or embossingtreatment to form irregularities on the surface is used as a carrier,the irregularities of the surface of the carrier are transferred ontothe surface of the resulting film, whereby a film having a lightdiffusion function can be produced. As a matter of course, by directlysubjecting a film to sand matting treatments the film can be impartedwith a light diffusion function.

Examples of methods to apply the film-forming solution include a methodof using a die or a coater, a spraying method, a brushing method, a rollcoating method, a spin coating method and a dipping method.

By applying the film-forming solution repeatedly, a film thickness or asurface smoothness of the resulting film can be controlled.

The solution layer formed on the carrier is then subjected to solventremoval treatment by drying or the like. As the drying method, a dryingmethod generally used, such as a method of passing the carrier with thesolution layer through a drying oven by means of a large number ofrollers, can be utilized. However, if bubbles are produced withevaporation of the solvent in the drying process, properties of theresulting film are markedly deteriorated, and therefore, in order toavoid this, it is preferable that the drying process is divided intoplural (two or more) steps and the temperature or the air flow in eachstep are controlled.

Thereafter, a film obtained by the above drying is peeled from thecarrier, whereby an optical film of the invention can be obtained.

In the optical film thus obtained, the amount of a residual solvent isusually not more than 10% by weight, preferably not more than 5% byweight, more preferably not more than 1% by weight particularlypreferably not more than 0.5% by weight. If the amount of the residualsolvent in the film exceeds the upper limit of the above rangerdimensional change of the film with time becomes large when the film isused, so that such an amount is undesirable. Moreover, because of theresidual solvent, the glass transition temperature is lowered and heatresistance is also lowered occasionally so that such an amount isundesirable.

In the case where the optical film is used as a raw film of theretardation film of the invention it becomes particularly necessaryoccasionally to properly control the amount of the residual solvent inthe film to a value of the above range. More specifically in order toallow the film to stably and uniformly exhibit retardation by stretchorientation the amount of the residual solvent in the film is desired tobe in the range of usually 10 to 0.1% by weight, preferably 5 to 0.1% byweight, more preferably 1 to 0.1% by weight. By allowing a slight amountof a solvent to remain in the film, stretch orientation can be sometimesfacilitated or control of appearance of retardation can be sometimesfacilitated.

The optical film has a thickness of usually 0.1 to 3,000 μm, preferably0.1 to 1000 μm, more preferably 1 to 500 μm, most preferably 5 to 300 m.If the film is too thin, handling properties of the film are sometimeslowered. If the film is too thick it sometimes becomes difficult to windup the film into a roll.

The thickness distribution of the optical film is in the range of +20%,preferably 120%, more preferably ±5%, particularly preferably ±3%, basedon the mean value. The degree of variability of the thickness based on 1cm is usually not more than 10%, preferably not more than 5%, morepreferably not more than 1%, particularly preferably not more than 0.5%.By controlling the thickness distribution of the film to a value of theabove range, occurrence of non-uniformity of retardation in a filmobtained by stretch-orienting the optical film can be prevented.

By subjecting the optical film of the invention to stretching (stretchorientation), the optical film becomes a retardation film. For example,when an optical film composed of the thermoplastic resin composition ofthe invention is subjected to free end monoaxial stretching in a stretchratio of 1.1 to 5.0 times at a stretching temperature ranging from aglass transition temperature of the thermoplastic resin composition to atemperature of the glass transition temperature+20° C., a retardationfilm having a NZ coefficient of not less than 1.1 can be obtained. Thefree end monoaxial stretching used herein means a method of stretching afilm in a monoaxial direction without applying tension to otherdirections than the monoaxial direction to be stretched (stretchingdirection). The NZ coefficient is a value defined by the followingformula with the proviso that the film stretching direction is taken asan x-axis, the in-plane perpendicular direction to the x-axis is takenas a y-axis, and the direction perpendicular to the x-axis and they-axis (film thickness direction) is taken as a z-axis.

NZ coefficient=(n _(x) −n _(z))/(n _(x) −n _(y))

(n_(x): refractive index in the x-axis direction, n_(y): refractiveindex in the y-axis direction, n_(z): refractive index in the z-axisdirection)

The optical film from which a retardation film having a NZ coefficientof the above range is obtained is, for example, an optical film composedof a thermoplastic resin composition consisting of a vinyl-based polymerobtained by terpolymerization of p-isopropenylphenol, an aromatic vinylmonomer and a vinyl cyanide monomer, and a cycloolefin-based resin. Morespecifically, there can be mentioned an optical film composed of athermoplastic resin composition consisting of a vinyl terpolymer ofp-isopropenylphenol/styrene/acrylonitrile and a cycloolefin-based resin.In this vinyl-based copolymer, proportions of the structural units aredesirably as follows. That is to says it is desirable that based on 100%by weight of all the structural units, the proportion of the structuralunits derived from p-isopropenylphenol is in the range of 0.5 to 30% byweight, the proportion of the structural units derived from the aromaticvinyl monomer is in the range of 50 to 99% by weights and the proportionof the structural units derived from the vinyl cyanide monomer is in therange of 0.5 to 20% by weight in the above thermoplastic resincomposition, -he compounding ratio of the vinyl-based polymer to thecycloolefin resin (vinyl-based polymer/cycloolefin-based resin, byweight) is preferably in the range of 10/90 to 50/50.

Retardation Film

The retardation film of the invention can be produced by subjecting theabove-mentioned optical film to stretching (stretch orientation). By thestretching, molecular chains of the (copolymer for forming the film areregularly oriented in a given direct-on, whereby a function of impartingretardation to the transmitted light is exhibited. The expression“regularly oriented” used herein means that molecular chains of ahigh-molecular compound are regularly oriented in the monoaxialdirection or the biaxial directions of the film plane or in thethickness direction of the film, while in the case where a usualhigh-molecular compound (polymer) is molded into a film by meltextrusion, casting or the like, molecular chains of the high-molecularcompound are not arranged in a specific direction but are at randomthough it depends upon a magnitude of film strain produced in themolding process. The degrees of regularity of the orientation of thehigh-molecular compound are various and can be controlled by thestretching conditions.

The stretching method is specifically a monoaxial stretching method or abiaxial orientation method publicly known. That is to say, examples ofsuch stretching methods include crosswise monoaxial stretching bytentering, compression stretching between rolls, lengthwise monoaxialstretching using two pairs of rolls having different circumferencesbiaxial orientation combining crosswise monoaxial stretching andlengthwise monoaxial stretching, and stretching by inflation.

In case of the monoaxial stretching method, the stretching rate is inthe range of usually 1 to 5000%/min, preferably 50 to 1,000%/min, morepreferably 100 to 1,000%/min, particularly preferably 100 to 500%/min.

As the biaxial orientation method, a method of carrying out stretchingoperations in two directions intersecting each other at the same timeand a method of carrying out monoaxial stretching and then carrying outstretching in a direction different from the initial stretchingdirection are available. In these methods, the intersecting anglebetween the two stretching axes is not specifically restricted becauseit is determined according to the desired properties, but it is usuallyin the range of 120 to 60 degrees. The stretching rates in thestretching directions may be the same or different and are each in therange of usually 1 to 5,000%/min, preferably 50 to 1,000%/min, morepreferably 100 to 1,000%/min, particularly preferably 100 to 500%/min.

The temperature in the stretching is not specifically restricted.However, if the glass transition temperature of the optical film(thermoplastic resin composition) used is taken as Tg, the stretchingtemperature is desired to be in the range of usually not lower than Tgand not higher than Tg+30° C., preferably not lower than Tg and nothigher than Tg+20° C., more preferably not lower than Tg and not higherthan Tg+10° C. When the stretching temperature is in the above range,large retardation can be exhibited, occurrence of non-uniformity ofretardation can be inhibited, and control of index ellipsoid can beeasily made, so that such a temperature is favorable.

The stretch ratio is not specifically restricted because it isdetermined according to various properties such as desired retardation.However, it is in the range of usually 1.01 to 10 times, preferably 1.03to 5 times, more preferably 1.03 to 3 times.

Although the film having been stretched in the above manner may becooled as it is at room temperature, it is desirable that the film isheld in an atmosphere of about not lower than Tg−100° C. and not higherthan Tg for at least 10 seconds, preferably 30 seconds to 60 minutes,more preferably 1 minute to 60 minutes, to perform heat setting and thencooled to room temperature, whereby a retardation film less suffering achange in retardation of transmitted light with time and having stableretardation properties is obtained.

In the retardation film obtained as above, molecules are oriented bystretching and thereby retardation is imparted to the transmitted light.The absolute value of the retardation can be controlled by controllingthe stretch ratio, the film thickness before stretching etc. Forexample, even if films have the same thickness as each other beforestretching, a film having a higher stretch ratio tends to provide alarger absolute value of retardation of the transmitted light.Therefore, by changing the stretch ratio, a retardation film capable ofimparting desired retardation to the transmitted light can be obtained.Further, even if films have the same stretch ratio as each other a filmhaving a larger thickness before stretching tends to provide a largerabsolute value of retardation of the transmitted light. Therefore, bychanging the film thickness before stretching a retardation film capableof imparting desired retardation to the transmitted light can beobtained.

For example, by subjecting an optical film composed of -he thermoplasticresin composition of the invention to free end monoaxial stretching in astretch ratio of 1.1 to 5.0 times at a stretching temperature rangingfrom a glass transition temperature of the thermoplastic resincomposition to a temperature of the glass transition temperature+20° C.,a retardation film having a NZ coefficient of usually not less than 1.10preferably not less than 1.12 can be obtained.

In the retardation film produced by stretching under the aboveconditions, a retardation value (R₄₀₀) at a wavelength of 400 nm, aretardation value (R₅₅₀) at a wavelength of 550 nm and a retardationvalue (R₈₀₀) at a wavelength of 800 nm desirably satisfy a relationshipof R₄₀₀<R₅₅₀<R₈₀₀.

The value of retardation imparted by the retardation film obtained asabove to -he transmitted light is determined according to the useapplication and is not determined indiscriminately. However, when theretardation film is used for a liquid crystal display device, anelectroluminescence display device or a wavelength plate of laseroptical system, the retardation value is in the range of usually 1 to10,000 nm, preferably 10 to 2,000 nm, more preferably 15 to 1,000 nm.

The retardation of a light transmitted by the film preferably has highuniformity and specifically the dispersion at a light wavelength of 550nm is desired to be usually in the range of ±20% preferably ±10%, morepreferably 15%. If the dispersion of retardation is out of the range of±20%, a liquid crystal device using the film suffers colornon-uniformity and there sometimes occurs a problem that the performanceof the display main body is lowered.

Further, the retardation of a light transmitted by the film depends upona wavelength of the transmitted light. The retardation film of theinvention preferably has reciprocal wavelength dispersion properties.Specifically, the ratio (R₆₆₀/R₅₅₀) of a retardation value (R₆₆₀) at awavelength of 660 nm to a retardation value (R₅₅₀) at a wavelength of550 nm is usually not less than 1.02, preferably not less than 1.03. Aretardation film having a R₆₆₀/R₅₅₀ ratio of less than theabove-mentioned lower limit sometimes lacks sharpness.

Furthermore, the retardation appearance (birefringence value) Δn of theretardation film of the invention is usually not less than 0.0005preferably not less than 0.0010, more preferably not less than 0.0015,at a wavelength of 550 nm. If the Δn is less than the above-mentionedlower limit, the film thickness needs to be increased in order that thefilm imparts retardation to the transmitted light, and in case of a filmof a large film thickness, light transmittance is lowered, or the dryingtime in the film production process is prolonged and as a result, filmproductivity is sometimes lowered.

The retardation film of the invention can be used as a single film or alaminate of two or more films, or can be used by laminating the film ona transparent substrate. Further, the film can be used also bylaminating it on another film, a sheet or a substrate.

For laminating the retardation film, an adhesive or a bonding materialis employable. As the adhesive or the bonding material, one havingexcellent transparency is preferably employed. Examples of suchadhesives or bonding materials include adhesives, such as naturalrubbers, synthetic rubbers, a vinyl acetate/vinyl chloride copolymer,polyvinyl ether, acrylic resins and modified polyolefin-based resins;curing type adhesives obtained by adding a curing agent, such as anisocyanate group-containing compound, to the above resins having afunctional group such as a hydroxyl group or an amino group;polyurethane-based adhesives for dry laminate; synthetic rubber-basedadhesives; and epoxy-based adhesives.

In order to enhance workability in laminating the retardation film onanother film, a sheet, a substrate or the like, an adhesive layer or abonding material layer may be laminated in advance on the retardationfilm. In the case where the adhesive layer or the bonding material layeris laminated, the aforesaid adhesive or bonding material is employableas the adhesive or the bonding material.

The optical film and the retardation film of the invention can be usedfor various liquid crystal display devices, such as cell phones, digitalinformation terminals, pocket bells, navigation systems, on-vehicleliquid crystal displays, liquid crystal monitors, dimmer panels,displays for GA machines and displays for AV machines,electroluminescence display devices touch panels, etc. Moreover they areuseful as wavelength plates used for recording/reproducing apparatusesof optical discs, such as CD, CD-R, MD, MO and DVD.

EXAMPLES

The present invention is further described with reference to thefollowing examples but it should be construed that the invention is inno way limited to those examples.

<Measuring and Evaluation Methods> (I) Intrinsic Viscosity [η]

A chlorobenzene solution having a concentration of 0. g/100 ml wasprepared, and an intrinsic viscosity was measured under the conditionsof 30° C.

(2) Molecular Weight

Using HLC-8220 gel permeation chromatograph (GPC, manufactured by TosohCorporation, column: T-SKgelg7000HxL, TSKgelCMHxL, TSKgelCMHxL andTSKgel-2000xL, manufactured by Tosoh Corporation), a number-averagemolecular weight (Mn), a weight-average molecular weight (Mw) and amolecular weight distribution (Mw/Mn), in terms of polystyrene weremeasured in a tetrahydrofuran (THF) solvent

(3) Glass Transition Temperature

Using DSC6200 (manufactured by Seiko Instruments Inc.) a glasstransition temperature was measured in a stream of nitrogen at a heatingrate of 20° C./min. Tg was determined in the following manner. A maximumpeak temperature (A point) of derivative differential scanning caloriesand a temperature (B point) obtained by subtracting 20° C. from themaximum peak temperature were plotted on a differential scanning caloriecurve, and the glass transition temperature was determined as anintersecting point between a tangent on a base line having the B pointas a starting point and a tangent on a base line having the A point as astarting point

(4) Reaction Conversion Ratio

Into an aluminum foil weighed in advance, 1.0 g of a solution obtainedafter polymerization was withdrawn, and the solution was heated on a hotplate at 220° C. for 30 minutes to evaporate a volatile content, wherebya solids concentration was determined. Then, a reaction conversion ratioof a monomer was measured in accordance with the following formula.

Reaction conversion ratio(%)=(solids concentration×total weight ofsolution−weight of catalyst used)/total weight of monomer used×100

(5) Compositional Analysis

In d-chloroform, 1.0 g of a sample was dissolved, and to the resultingsolution, 50 mg of chromium(III) acetylacetonate was added. Then, usinga nuclear magnetic resonance spectrometer (NMR, AVANCE500 manufacturedby Bruker), ¹³C-NMR of a vinyl-based copolymer was measured. From thepeak (153 ppm) area intensity of an aromatic ring carbon derived fromp-ispropenylphenol and the peak (142-150 ppm) area intensity ofquaternary carbon derived from styrene, proportions of structural unitsderived from styrene and structural units derived fromp-isopropenylphenol were calculated.

(6) Stress Optical Coefficient (C_(R))

A stress optical coefficient was measured by a publicly known method(Polymer Journal, vol. 27, No. 9, pp. 943-950 (1995).

That is to say, the resulting thermoplastic resin composition wassubjected to film formation using a methylene chloride casting methodand then vacuum dried at 100° C. for 24 hours to prepare a film.Thereafter, 4 specimens each having a size of 0.5 mm×5 mm×50 mm wereprepared and to the specimens were each applied different loads (4points) of 10 to 300g. Then, the specimens were placed in a heating ovenat a temperature of Tg of the specimens+20° C. and allowed to stand for30 minutes to stretch them. Thereafter, the heating oven was slowlycooled to room temperature while the loads were applied, and retardationvalues of the stretched specimens were each measured in the followingmanner.

A retardation value (550 nm) was measured by the use of an automaticbirefringence meter (manufactured by Oji Scientific Instruments,KOBRA-21ADH). A stress (C) and a birefringence value (ΔN) of eachspecimen were determined in accordance with the following formulas, andfrom an inclination of a σ−ΔN plot, C_(R) was determined.

σ=F/(d·w)

(F: load, d: thickness of specimen after stretching, w: width ofspecimen after stretching)

ΔN=Re/d

(Re: retardation value), d: thickness of specimen after stretching)

C _(R) =ΔN/σ (unit: Br=10⁻¹² Pa⁻¹)

(7) Retardation Value of Injection Molded Product

A retardation value (at 550 nm) of a gate center of a specimen forbirefringence evaluation was measured by the use of an automaticbirefringence meter (manufactured by Oji Scientific Instruments,KOBRA-21ADH).

(8) Water Resistance (Measurement of Water Absorption)

A specimen for water resistance evaluation was dried at 100° C. for 24hours, and then a weight W₀ of the specimen was measured. Subsequently,the specimen was immersed in water at 23° C. for 24 hours, and then aweight W₁ of the specimen was measured, followed by calculation of waterabsorption from the following formula.

Water absorption(%)=[(W ₁ −W ₀)/W ₀]×100

(9) Transparency (Measurement of Total Light Transmittance)

A total light transmittance of a specimen for transparency evaluationwas measured in accordance with JIS K7105 (measuring method A) using ahaze meter (manufactured by Suga Test Instrument Co., Ltd., HGM-2DP).

(10) Haze

A haze of the resulting film was measured in according with JIS K7105(measuring method A) using a haze meter (manufactured by Suga TestInstrument Co., Ltd., HGM-2DP).

(11) Retardation Value, Birefringence Value, Reciprocal WavelengthDispersion and NZ Coefficient of Retardation Film

Retardation value at 550 nm and 660 nm and a NZ coefficient of a filmafter stretching were measured by the use of an automatic birefringencemeter (manufactured by Oji Scientific Instruments, KOBRA-21ADH). The NZcoefficient is a value determined by the following formula.

NZ coefficient=(n _(x) −n _(z))/(n _(x) −n _(y))

(n_(x): refractive index in x-axis direct-on, n_(y): refractive index iny-axis direction, n_(z): refractive index in z-axis direction)

A birefringence value and a reciprocal wavelength dispersion of theretardation film were determined by the following formulas.

Birefringence value(Δn)=R ₅₅₀ /d

Reciprocal wavelength dispersion=R ₆₆₀ /R ₅₅₀

(R₅₅₀, R₆₆₀: retardation value at wavelengths of 550 nm and 660 nm, d:film thickness)

(12) Tear Strength

Tear strength of a film after stretching was measured in accordance withJIS K6772.

(13) Film Colorability

A film after stretching was held at 80° C. for 1000 hours and thensubjected to heat resistance test. Yellowness (YI) of the film wasmeasured before and after the test in accordance with JIS K 7105 using aspectrophotometer (manufactured by Suga Test Instrument Co., Ltd.).Then, a change in YI between before and after the test (YI=YI after thetest−YI before the test) was calculated.

(14) Amount of Residual Solvent

The resulting film was dissolved in a solvent, and an amount of aresidual solvent was measured by gas chromatography.

Preparation Example 1

In a reaction vessel purged with nitrogen, 100 parts by weight of8-methyl-8-methoxycarbonyltetracyclo[4.4.0.1^(2,5).1^(7,10)]-dodecenerepresented by the following formula as a specific monomer-4 parts byweight of 1-hexane as a molecular weight modifier and 200 parts byweight of toluene as a solvent were placed, and they were heated to 80°C.

Then, 0.12 part by weight of a toluene solution of triethylaluminum(concentration: 0.6 mol/l) and 0.37 part by weight of a toluene solutionof methanol-modified WCl₆ (concentration: 0.025 mol/l) were added, andreaction was performed at 80° C. for 1 hour to obtain a polymer.

The resulting solution of the polymer was placed in an autoclave, then200 parts by weight of toluene as a solvent and 0.06 part by weight ofRuHCl(CO)[P(C₆H₅)₃]₃ as a hydrogenation catalyst were added, andthereafter, purging with nitrogen was carried out three times. Then, ahydrogen gas was introduced into the reaction vessel to adjust thepressure to 8.0 MPa. Thereafter, the reaction vessel was heated to 165°C., and with maintaining the pressure at 10 MPa, reaction was performedat 165° C. for 3 hours to obtain a hydrogenation product. Thehydrogenation product was reprecipitated with methanol, and theprecipitate was recovered and then dried to obtain a cycloolefin-basedpolymer (1).

This cycloolefin-based polymer (1) had an intrinsic viscosity [η] of0.78 dl/g, a weight-average molecular weight (Mw) of 11.5×10⁴, molecularweight distribution (Mw/Mn) of 3.3 and a glass transition temperature(Tg) of 167° C. The degree of hydrogenation of the cycloolefin-basedpolymer (1) was determined by ¹H-NMR measurement, and as a result, notless than 99.9% of the olefinic unsaturated bonds in the main chain hadbeen hydrogenated.

Preparation Example 2

In a reaction vessel, 96.8 parts by weight of styrene, 3.2 parts byweight of p-opropenylphenol, 30 parts by weight of cyclohexane and 0.64part by weight of 2D2-bis(4,4-di-tert-butylperoxycyclohexyl)propane(available from Nippon Oils and Fats Corporation, Pertetra A) wereplaced. Through the contents in the reaction vessel, a stream ofnitrogen was bubbled for 10 minutes, and then reaction was performed at95° C. for 8 hours to obtain a styrene/p-isopropenylphenol copolymer(2).

The copolymer (2) had a reaction conversion ratio, as measured by asolids content measurement, of 98%, a weight-average molecular weight(Mw) of 78000, a number-average molecular weight (Mn) of 35500, amolecular weight distribution (Mw/Mn) of 2.2 and a glass transitiontemperature (Tg) of 103° C. A ¹³C-NMR spectrum of the copolymer (2) isshown in FIG. 1 (general view) and FIG. 2 (enlarged view). Peaks ofcarbons (i) to (iv) of the aromatic ring derived fromp-isopropenylphenol were confirmed to be present at 115.2 ppm, 122.6ppm, 138.4 ppm and 153.1 ppm, respectively. From integral values of thepeak of the carbon (iv) and a peak (145.2 ppm) of quaternary carbonderived from polystyrene, composition of the copolymer was determined.As a result, a ratio of structural units derived from styrene/structuralunits derived from p-isopropenylphenol in the copolymer (2) was 96.8/3.2(by weight).

Preparation Example 3

In a reaction vessel, 91.5 parts by weight of styrene, 4.5 parts byweight of p-isopropenylphenol, 4.0 parts by weight of acrylonitrile and0.61 part by weight of 2,2′-azobis(2,4-dimethylvaleronitrile, (availablefrom Wako Laboratory Chemicals, V-65.) were placed. Through the contentsin the reaction vessel, a stream of nitrogen was bubbled for 10 minutes,and then reaction was performed at 55° C. for 7 hours. After thereaction was completed the reaction product was reprecipitated with alarge amount of methanol to obtain astyrene/p-isopropenylphenol/acrylonitrile copolymer (3).

The copolymer (3) had a reaction conversion ratio, as measured by asolids content measurement, of 73%, Mw of 72700, Mn of 40200, Mw/Mn of1.81 and a glass transition temperature (Tg) of 110° C. From a ¹³C-NMRspectrum of the copolymer (3) composition of the copolymer wasdetermined. As a result a ratio of structural units derived fromstyrene/structural units derived from p-isopropenylphenol/structuralunits derived from acrylonitrile in the copolymer (3) was 91.4/4.5/4.1(by weight).

Preparation Example 4

A styrene/p-tert-butoxystyrene copolymer was obtained in the same manneras in Preparation Example 2, except that instead of p-isopropenylphenol,p-tert-butoxystyrene was used in an amount equimolar with styrene. Tothe copolymer, 0.2 part by weight of p-toluenesulfonic acid was added,and deblocking reaction was performed at 100° C. for 4 hours to obtain astyrene/p-hydroxystyrene copolymer (4).

The copolymer (4) had Mw of 83000, Mn of 37700, Mw/Mn of 2.2 and a glasstransition temperature (Tg) of 103° C.

Example 1

The polymer (1) and the copolymer (2) were melt-mixed in a mixing ratioof 65/35 (polymer (1)/copolymer (2), by weight) at 300° C. to obtain athermoplastic resin composition. A stress optical coefficient (C_(R)value) of the thermoplastic resin composition was measured in theaforesaid manner.

The thermoplastic resin composition was dried by a vacuum dryer underthe conditions of 100° C. and 4 hours, and then injection molded bymeans of an injection molding machine “SG75M-S” (manufactured bySumitomo Heavy Industries, Ltd., cylinder diameter: 28 mm, clampingforce: 75 t) under the conditions of a resin temperature of 300° C., amold temperature of 130° C. and an injection rate of 100 mm/sec andunder the conditions such that the hopper and the cylinder were filledwith nitrogen. Thus, a specimen for birefringence evaluation (injectionmolded strip having width of 60 mm, length of 80 mm and thickness of 1mm), a specimen for water resistance evaluation (width: 40 mm, length:80 mm, thickness: 3 mm) and a specimen for transparency evaluation(thickness: 3 mm) were prepared. These specimens were evaluated onretardation value at 550 nm, water resistance and transparency. Theresults are set forth in Table 1.

Further, the polymer (1) and the copolymer (2) were dissolved in a ratioof 65/35 (polymer (1)/copolymer (2), by weight) in methylene chloride toprepare a solution having a concentration of 30% by weight, and thesolution was subjected to film formation using a solvent casting methodand then vacuum dried at 100° C. for 48 hours to prepare a transparentfilm having a film thickness of 175 μm. The result of differentialscanning calorimetry (DSC) of the transparent film is shown in FIG. 3.This transparent film had single Tg of 137° C. and a haze of 0.1. Fromthis, it was confirmed that the polymer (1) and the copolymer (2) hadbeen compatibilized with each other.

The transparent film was cut into a size of 10 mm×80 mm, and the thuscut film was stretched in a stretch ratio of 2.0 times by he use of anInstron tensile tester (5567 type) equipped with a constant temperaturebath through free end monoaxial stretching under the conditions of astretching temperature of Tg+5° C. (=142° C.), a stretching rate of 60mm/min (120%/min) and a chuck distance of 50 mm, to obtain a film havinga film thickness of 123 m. The film after stretching was evaluated onhaze, retardation value at 550 nm, birefringence value at 550 nm,reciprocal wavelength dispersion (R₆₆₀/R₅₅₀), NZ coefficient, tearstrength, film colorability after heat resistance test and amount of aresidual solvent. The results are set forth in Table 1.

Example 2

A thermoplastic resin composition was obtained in the same manner as inExample 1, except that instead of the copolymer (2), the copolymer (3)was mixed with the polymer (1) in a mixing ratio of 65/35 (polymer(1)/copolymer (3), by weight) A stress optical coefficient (C_(R) value)of the thermoplastic resin composition was measured in the aforesaidmanner.

From the thermoplastic resin composition, various specimens wereprepared in the same manner as in Example 1, and the specimens wereevaluated on retardation value at 550 nm, water resistance andtransparency. The results are set forth in Table 1.

Further, a transparent film having a film thickness of 175 μm wasobtained in the same manner as in Example 1, except that instead of thecopolymer (23, the copolymer (3) was dissolved in a ratio of 65/35(polymer (1)/copolymer (3), by weight) in methylene chloride. Thetransparent film had single Tg of 138° C. and a haze of 0.1. From thisit was confirmed that the polymer (1) and the copolymer (3) had beencompatibilized with each other.

The transparent film was cut into a size of 10 mm×80 mm, and the thuscut film was stretched in a stretch ratio of 2.0 times by the use of anInstron tensile tester (5567 type) equipped with a constant temperaturebath through free end monoaxial stretching under the conditions of astretching temperature of Tg+5° C. (=143° C.), a stretching rate of 60mm/min (120%/min) and a chuck distance of 50 mm, to obtain a film havinga film thickness of 121 μm. The film after stretching was evaluated onhaze, retardation value at 550 nm, birefringence value at 550 nm,reciprocal wavelength dispersion (R₆₆₀/R₅₅₀) NZ coefficient, tearstrength, film colorability after heat resistance test and amount of aresidual solvent. The results are set forth in Table 1.

Example 3

A thermoplastic resin composition was obtained in the same manner as inExample 2, except that the mixing ratio of the polymer (1) to thecopolymer (3) was changed to 55/45 (polymer (1)/copolymer (3), byweight). A stress optical coefficient (C_(R) value) of the thermoplasticresin composition was measured in the aforesaid manner.

From the thermoplastic resin composition various specimens were preparedin the same manner as in Example 1, and the specimens were evaluated onretardation value at 550 nm, water resistance and transparency. Theresults are set forth in Table 1.

Further, a transparent film having a film thickness of 175 μm wasobtained in the same manner as in Example 2, except that the ratio ofthe polymer (1) to the copolymer (3) was changed to 55/45 (polymer(1)/copolymer (3) by weight). The transparent film had single Tg of 123°C. and a haze of 0.1. From this, it was confirmed that the polymer (1)and the copolymer (3) had been compatibilized with each other.

The transparent film was cut into a size of 10 mm×80 mm and the thus cutfilm was stretched in a stretch ratio of 2.0 times by the use of anInstron tensile tester (5567 type) equipped with a constant temperaturebath through free end monoaxial stretching under the conditions of astretching temperature of Tg+5° C. (=128° C.), a stretching rate of 60mm/min (120%/min) and a chuck distance of 50 mm, to obtain a film havinga film thickness of 123 μm. The film after stretching was evaluated onhaze, retardation value at 550 nm, birefringence value at 550 nm,reciprocal wavelength dispersion (R₆₆₀/R₅₅₀), NZ coefficient, tearstrength, film colorability after heat resistance test and amount of aresidual solvent. The results are set forth in Table 1.

Comparative Example 1

A stress optical coefficient (C_(R) value) of the polymer (1) wasmeasured in the aforesaid manner.

From the polymer (1), various specimens were prepared in the same manneras in Example 1, and the specimens were evaluated on retardation valueat 550 nm, water resistance and transparency. The results are set forthin Table 1.

Further, the polymer (1) was dissolved in methylene chloride to preparea solution having a concentration of 30% by weight, and the solution wassubjected to film formation using a solvent casting method and thenvacuum dried at 100° C. for 48 hours to prepare a transparent filmhaving a film thickness of 175 μm. This transparent film had Tg of 167°C. and a haze of 0.1.

The transparent film was cut into a size of 10 mm×80 mm, and the thuscut film was stretched in a stretch ratio of 2.0 times by the use of anInstron tensile tester (5567 type) equipped with a constant temperaturebath through free end monoaxial stretching under the conditions of astretching temperature of Tg+5° C. (=172° C.), a stretching rate of 60mm/min (120%/min) and a chuck distance of 50 mm, to obtain a film havinga film thickness of 123 μm. The film after stretching was evaluated onhaze, retardation value at 550 nm, birefringence value a 550 nm,reciprocal wavelength dispersion (R₆₆₀/R₅₅₀), NZ coefficients tearstrengths film colorability after heat resistance test and amount of aresidual solvent. The results are set forth in Table 1.

Comparative Example 2

A thermoplastic resin composition was obtained in the same manner as inExample 1, except that instead of the copolymer (2), the copolymer (4)was mixed with the polymer (1) in a mixing ratio of 65/35 (polymer(1)/copolymer (4), by weight). A stress optical coefficient (C_(R)value) of the thermoplastic resin composition was measured in theaforesaid manner.

From the thermoplastic resin composition, various specimens wereprepared in the same manner as in Example 1, and the specimens wereevaluated on retardation value at 550 nm, water resistance andtransparency. The results are set forth in Table 1.

Further, a transparent film having a film thickness of 175 μm wasobtained in the same manner as in Example 1, except that instead of thecopolymer (2), the copolymer (4) was dissolved in a ratio of 65/35(polymer (1)/copolymer (4), by weight) in methylene chloride. Thetransparent film had single Tg of 132° C. and a haze of 0.1. From this,it was confirmed that the polymer (1) and the copolymer (4) had beencompatibilized with each other.

The transparent film was cut into a size of 10 mm×80 mm and the thus cutfilm was stretched in a stretch ratio of 2.0 times by the use of anInstron tensile tester (5567 type) equipped with a constant temperaturebath through free end monoaxial stretching under the conditions of astretching temperature of Tg+5° C. (=137° C.), a stretching rate of 60nm/min (120%/min) and a chuck distance of 50 mm, to obtain a film havinga film thickness of 119 μm. The film after stretching was evaluated onhaze, retardation value at 550 nm, birefringence value at 550 nm,reciprocal wavelength dispersion (R₆₀/R₅₅₀) NZ coefficient, tearstrength, film colorability after heat resistance test and amount of aresidual solvent. The results are set forth in Table 1.

Comparative Example 3

A thermoplastic resin composition was obtained in the same manner as inExample 1, except that instead of the copolymer (2), commerciallyavailable polystyrene (polystyrene manufactured by PS-Japan, Mw:219,000, Mn: 81,300) was used. Because the thermoplastic resincomposition was opaque, the stress optical coefficient could not bemeasured.

From the thermoplastic resin composition, various specimens wereprepared in the same manner as in Example 1, and the specimens wereevaluated on water resistance and transparency. The results are setforth in Table 1. Because these specimens were opaque, the retardationvalue at 550 nm could not be measured.

Further, a film having a film thickness of 175 μm was obtained in thesame manner as in Example 1 except that instead of the copolymer (2),commercially available polystyrene (polystyrene manufactured byPS-Japan, Mw: 219,000, Mn: 81,300) was used. The film was opaque and hadtwo Tg, namely, Tg of 167° C. which was derived from the polymer (1) andTg of 101° C. which was derived from polystyrene, and a haze of 94. Fromthis, it was confirmed that the polymer (1) and polystyrene had not beencompatibilized with each other, and optical properties could not bemeasured. From this it was confirmed that when commercially availablepolystyrene was used, the resulting film could not be used as an opticalmaterial.

The film was cut into a size of 10 mm×80 mm, and the thus cut film wasstretched in a stretch ratio of 2.0 times by the use of an Instrontensile tester (5567 type) equipped with a constant temperature baththrough free end monoaxial stretching under the conditions of astretching temperature of 172° C., a stretching rate of 60 mm/min(120%/min) and a chuck distance of 50 mm, to obtain a film having a filmthickness of 122 μm. The film after stretching was evaluated on tearstrength and amount of a residual solvent. The results are set forth inTable 1.

Comparative Example 4

A thermoplastic resin composition was obtained in the same manner as inExample 1, except that instead of the copolymer (2), commerciallyavailable polystyrene containing 7% by weight of maleic anhydride(manufactured by NOVA Chemicals Japan Ltd., Dylark, grade: D232, Mw:207,000, Mn: 104,000) was used. Because the thermoplastic resincomposition was opaque, the stress optical coefficient could not bemeasured.

From the thermoplastic resin composition, various specimens wereprepared in the same manner as in Example 1, and the specimens wereevaluated on water resistance and transparency. The results are setforth in Table 1. Because these specimens were opaque, the retardationvalue at 550 nm could not be measured.

Further, a film having a film thickness of 175 μm was obtained in thesame manner as in Example 1, except that instead of the copolymer (2),commercially available polystyrene containing 7% by weight of maleicanhydride (manufactured by NOVA Chemicals Japan Ltd, Dylark, grade:D232, Mw: 207,000, Mn: 104,000) was used. The film was opaque and hadtwo Tg, namely, Tg of 167° C. which was derived from the polymer (1) andTg of 120° C. which was derived from maleic anhydride-containingpolystyrene, and a haze of 88. From this, it was confirmed that thepolymer (1) and the maleic anhydride-containing polystyrene had not beencompatibilized with each other, and optical properties could not bemeasured.

The film was cut into a size of 10 mm×80 mm, and the thus cut film wasstretched in a stretch ratio of 2.0 times by the use of an Instrontensile tester (5567 type) equipped with a constant temperature baththrough free end monoaxial stretching under the conditions of astretching temperature of 172° C., a stretching rate of 60 mm/min(120%/min) and a chuck distance of 50 mm, to obtain a film having a filmthickness of 123 m. The film after stretching was evaluated on tearstrength and amount of a residual solvent. The results are set forth inTable 1.

Comparative Example 5

A transparent film having a film thickness of 175 μm was obtained in thesame manner as in Comparative Example 4, except that film formation wascarried out using a toluene solvent instead of methylene chloride. Thetransparent film had single Tg of 140° C. and a haze of 0.5. From this,it was confirmed that the polymer (1) and the 7 wt % maleicanhydride-containing polystyrene had been compatibilized with eachother.

The transparent film was cut into a size of 10 m×80 mm, and the thus cutfilm was stretched in a stretch ratio of 2.0 times by the use of anInstron tensile tester (5567 type) equipped with a constant temperaturebath through free end monoaxial stretching under the conditions of astretching temperature of Tg+5° C. (=145° C.), a stretching rate of 60mm/min (120%/min) and a chuck distance of 50 mm, to obtain a film havinga film thickness of 124 μm. The film after stretching was evaluated onhazes retardation value at 550 nm, birefringence value at 550 nm,reciprocal wavelength dispersion (R₆₆₀/R₅₅₀), NZ coefficient, tearstrengths film colorability after heat resistance test and amount of aresidual solvent. The results are set forth in Table 1. This stretchedfilm had a large amount of residual toluene, and appearance ofretardation was markedly deteriorated.

TABLE 1 Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 EX. 1 EX. 2 EX.3 EX. 4 EX. 5 Polymer (1) 65 65 55 100 65 65 65 65 Copolymer (2) 35Copolymer (3) 35 45 Copolymer (4) 35 Polystyrene 35 Maleicanhydride-containing polystyrene 35 35 Molded article C_(R) value 10501120 600 2200 1020 IM IM IM Retardation value (550 nm, unit: mm) 120 15050 250 120 IM IM IM Water absorption (%) 0.2 0.28 0.2 0.4 0.21 0.2 0.20.2 Total light transmittance (%) 94 94 94 94 94 2 3 3 Retardation filmHAZE (%) 0.1 0.1 0.1 0.1 0.1 94 89 0.5 Retardation value (550 nm, unit:mm) 221 211 64 492 202 IM IM 36 Birefringence value (550 nm) 0.001800.00174 0.00052 0.00400 0.00170 IM IM 0.00029 R₆₆₀/R₅₅₀ 1.02 1.02 1.070.98 1.02 IM IM 1.02 NZ coefficient 1.01 1.13 1.15 1.02 1.00 IM IM 1.04Tear strength (gf) 25 35 40 18 22 2 3 20 YI before test 0.1 0.1 0.1 0.10.1 IM IM 0.1 YI after test 0.2 0.2 0.2 0.2 4.6 IM IM 5 ΔYI 0.1 0.1 0.10.1 4.5 IM IM 4.9 Amount of residual solvent (ppm) 1 ppm 1 ppm 1 ppm 1ppm 1 ppm 1 ppm 1 ppm 1220 or less or less or less or less or less orless or less IM: Measurement could not be made because of opacity.

INDUSTRIAL APPLICABILITY

The thermoplastic resin composition of the invention is excellent inweathering resistance and heat resistance and can be preferably appliedto general optical uses, and besides, it can be preferably used byprocessing it into films or sheets. In particular, film formation usingmethylene chloride having a low boiling point is possible, so that incase of production of optical films by a solvent casting method, dryingat low temperatures becomes possible and heat deterioration in the filmproduction can be prevented, and the thermoplastic resin composition isoptimum for uses requiring stretching, for example, optical films suchas retardation films. Moreover, the resulting optical films areexcellent in weathering resistance and heat resistance, so that they canbe applied to uses whose usage environmental conditions are relativelysevere, such as navigation systems and on-vehicle liquid crystaldisplays.

As shown in Example 2 and Example 3, when the optical film of theinvention is subjected to free end monoaxial stretching, the NZcoefficient becomes more than 1.1, so that even if the film is notsubjected to biaxial orientation, a stretched film having a NZcoefficient of not less than 1.1 can be obtained. From the above resultsit can be seen that also in the case where the optical film of theinvention is subjected to width-constraint monoaxial stretching orbiaxial stretching, a stretched film having a larger NZ coefficient thana stretched film obtained from an optical film composed of aconventional cycloolefin ring-opened (co)polymer is obtained.Accordingly, by the use of the optical film of the invention, astretched film having a larger NZ coefficient than a stretched filmobtained from a conventional optical film can be easily produced, and aNZ coefficient of a stretched film can be easily controlled withoutusing special stretching technique.

Further, the stretched film of the invention exhibits specificwavelength dispersion properties (reciprocal wavelength dispersionproperties) of R₄₀₀<R₅₅₀<R₈₀₀. These wavelength dispersion propertiescan be controlled by composition of the vinyl-based (co)polymer andcompounding ratio between the cycloolefin-based resin and thevinyl-based (co)polymer, and there can be provided by the invention amaterial exhibiting wavelength dispersion properties of desiredbirefringence (or retardation) required for molded articles such asstretched films.

1. A thermoplastic resin composition comprising: (A) a cycloolefln-basedpolymer, and (B) a vinyl-based polymer having a structural unit derivedfrom p-isopropenylphenol.
 2. The thermoplastic resin composition asclaimed in claim 1, wherein the cycloolefin-based polymer (A) has astructural unit represented by the following formula (1):

wherein R¹ to R⁴ are each independently a hydrogen atom, a halogen atom,a substituted or unsubstituted hydrocarbon group of 1 to 30 carbon atomswhich may have a linkage containing oxygen, nitrogen, sulfur or silicon,or a polar group; R¹ and R², or R³ and R⁴ may be bonded to each other toform a monocyclic or polycyclic carbon ring or hetrocyclic ring; X isindependently —CH═CH— or —CH₂CH₂—; m is 0, 1 or 2; and p is 0 or
 1. 3.The thermoplastic resin composition as claimed in claim 1, wherein thevinyl-based polymer (B) further has a structural unit derived from anaromatic vinyl-based monomer other than p-isopropenylphenol.
 4. Thethermoplastic resin composition as claimed in claim 3, wherein thevinyl-based polymer (B) further has a structural unit derived from avinyl cyanide-based monomer.
 5. An optical film comprising: (A) acycloolefin-based polymer, and (B) a vinyl-based polymer having astructural unit derived from p-isopropenylphenol.
 6. An optical filmcomprising a thermoplastic resin composition comprising (A) acycloolefin-based polymer and (B) a vinyl-based polymer having astructural unit derived from p-isopropenylphenol, and having thefollowing properties: when the optical film is subjected to free endmonoaxial stretching in a stretch ratio of 1.1 to 5.0 times at astretching temperature ranging from a glass transition temperature ofthe thermoplastic resin composition to a temperature of the glasstransition temperature+20° C., a NZ coefficient of the resulting filmbecomes not less than 1.1.
 7. A retardation film obtained bystretch-orienting the optical film of claim 5 or
 6. 8. A retardationfilm obtained by subjecting an optical film comprising a thermoplasticresin composition which comprises (A) a cycloolefin-based polymer and(B) a vinyl-based polymer having a structural unit derived fromp-isopropenylphenol to free end monoaxial stretching in a stretch ratioof 1.1 to 5.0 times at a stretching temperature ranging from a glasstransition temperature of the thermoplastic resin composition to atemperature of the glass transition temperature+20° C., and having a NZcoefficient of not less than 1.1.